Mitochondrial shuttlesystem as a duagrams

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Here is a complete, diagram-rich breakdown of the two mitochondrial shuttle systems.

Mitochondrial Shuttle Systems

The inner mitochondrial membrane (IMM) is impermeable to NADH. Cytosolic NADH produced by glycolysis cannot directly enter the mitochondrial matrix to donate electrons to Complex I. Two shuttle systems solve this problem by transferring the reducing equivalents (not NADH itself) across the IMM.

1. Glycerol 3-Phosphate Shuttle

Found in: Skeletal muscle, brain (most tissues) ATP yield: ~1.5 ATP per cytosolic NADH

Diagram (Basic Medical Biochemistry, Fig. 24.9):

Diagram (Lippincott Biochemistry, Fig. 6.17A - with chemical structures):

Glycerol 3-phosphate shuttle - Lippincott

Steps:

Step	Location	Reaction
1	Cytosol	DHAP + NADH + H+ → Glycerol 3-P + NAD+ (cytosolic glycerol 3-P dehydrogenase)
2	Glycerol 3-P diffuses	Passes through outer membrane to the IMM surface
3	IMM (outer face)	Glycerol 3-P + FAD → DHAP + FADH2 (mitochondrial glycerol 3-P dehydrogenase)
4	DHAP returns	Back to cytosol to continue the shuttle
5	FADH2	Donates electrons to CoQ → ETC → ~1.5 ATP

Net equation:

NADH(cytosol) + FAD(mitochondria) → NAD+(cytosol) + FADH2(mitochondria)

Key point: Electrons enter the ETC at CoQ (bypassing Complex I), so only ~1.5 ATP are generated - fewer than the malate-aspartate shuttle. This shuttle is irreversible and operates in a unidirectional fashion.

2. Malate-Aspartate Shuttle

Found in: Heart, liver, kidney (most aerobic tissues except skeletal muscle and brain) ATP yield: ~2.5 ATP per cytosolic NADH

Diagram (Basic Medical Biochemistry, Fig. 24.10):

Diagram (Lippincott Biochemistry, Fig. 6.17B - matrix side detail):

Steps (6-step cycle):

Step	Location	Reaction
1	Cytosol	OAA + NADH + H+ → Malate + NAD+ (cytosolic malate dehydrogenase)
2	IMM transporter	Malate enters matrix via malate-α-ketoglutarate exchanger
3	Matrix	Malate + NAD+ → OAA + NADH (mitochondrial malate dehydrogenase) → NADH feeds Complex I
4	Matrix	OAA + Glutamate → Aspartate + α-KG (aspartate aminotransferase / transamination)
5	IMM transporter	Aspartate exits via glutamate-aspartate exchanger; α-KG exits via malate-α-KG exchanger
6	Cytosol	Aspartate + α-KG → OAA + Glutamate (cytosolic aspartate aminotransferase) → OAA restarts cycle

Net equation:

NADH(cytosol) + NAD+(matrix) → NAD+(cytosol) + NADH(matrix)

Key transporters in the IMM:

Malate-α-ketoglutarate exchanger - imports malate, exports α-KG
Glutamate-aspartate exchanger - imports glutamate, exports aspartate

Comparison Table

Feature	Glycerol 3-P Shuttle	Malate-Aspartate Shuttle
Tissues	Skeletal muscle, brain	Heart, liver, kidney
Electron acceptor	FAD	NAD+
ETC entry point	CoQ (Complex II level)	Complex I
ATP yield	~1.5 ATP/NADH	~2.5 ATP/NADH
Reversibility	Irreversible	Reversible
Cofactor regenerated	NAD+ in cytosol	NAD+ in cytosol
Carriers used	DHAP / Glycerol 3-P	Malate, Aspartate, Glutamate, α-KG

Why Two Shuttles?

The glycerol 3-P shuttle is faster and simpler but less efficient (yields less ATP). It is favored in tissues that need rapid NAD+ regeneration even at the cost of ATP yield (e.g., during intense exercise in muscle).

The malate-aspartate shuttle is more efficient but requires 6 steps and two membrane transporters. It is favored in highly aerobic tissues (heart, liver) where maximizing ATP yield per glucose is the priority.

The overall ATP yield from one glucose depends on which shuttle is used:

With glycerol 3-P shuttle: ~30 ATP per glucose
With malate-aspartate shuttle: ~32 ATP per glucose

(Basic Medical Biochemistry - A Clinical Approach 6e, p. 875-876; Lippincott Illustrated Reviews Biochemistry 8e, Fig. 6.17)

Maje it simple

Mitochondrial Shuttle Systems — Simplified

The Core Problem

Glycolysis makes NADH in the cytosol, but the ETC is inside the mitochondria. NADH cannot cross the inner mitochondrial membrane. So the cell uses shuttle systems to sneak the electrons in.

Shuttle 1 — Glycerol 3-Phosphate Shuttle

"The Fast but Cheap Shuttle"

Think of it as: NADH passes its electrons to DHAP → becomes Glycerol 3-P → crosses membrane → drops electrons onto FAD → FADH₂ feeds the ETC.

Cytosol:      DHAP  +  NADH  →  Glycerol 3-P  +  NAD⁺
                                      ↓ (crosses membrane)
Mitochondria: Glycerol 3-P  +  FAD  →  DHAP  +  FADH₂  →  ETC


Found in	Skeletal muscle, brain
ATP made	~1.5 ATP per NADH
Why less ATP?	Electrons skip Complex I, enter at CoQ

Shuttle 2 — Malate-Aspartate Shuttle

"The Slow but Efficient Shuttle"

Think of it as: NADH passes electrons to Oxaloacetate → becomes Malate → crosses membrane → drops electrons back onto NAD⁺ (making NADH inside) → feeds Complex I directly.

Cytosol:      OAA  +  NADH  →  Malate  +  NAD⁺
                                   ↓ (crosses membrane)
Mitochondria: Malate  +  NAD⁺  →  OAA  +  NADH  →  Complex I → ETC

(OAA can't cross back directly, so it becomes Aspartate → exits → reforms OAA in cytosol)


Found in	Heart, liver, kidney
ATP made	~2.5 ATP per NADH
Why more ATP?	NADH enters at Complex I

Side-by-Side Summary

	Glycerol 3-P Shuttle	Malate-Aspartate Shuttle
Speed	Fast	Slower
ATP yield	1.5	2.5
Electron carrier into mito	Glycerol 3-P	Malate
Electron acceptor inside	FAD	NAD⁺
Tissue	Muscle, Brain	Heart, Liver, Kidney

Bottom line: Both shuttles do the same job — get cytosolic NADH electrons into the mitochondria. The malate-aspartate shuttle is more efficient (2.5 ATP vs 1.5 ATP), while the glycerol 3-P shuttle is simpler and faster.

Create a comparison diagram poster (glycerol 3-P vs malate-aspartate)

Generating Image

A clean educational biochemistry comparison poster showing two mitochondrial shuttle systems side by side. LEFT SIDE - "Glycerol 3-Phosphate Shuttle" (blue theme): - Label at top: "GLYCEROL 3-PHOSPHATE SHUTTLE" - Subtitle: "Fast • Less Efficient • Muscle & Brain" - Show CYTOSOL section at top and MITOCHONDRIAL MATRIX at bottom, separated by a membrane (labeled "Inner Mitochondrial Membrane") - In cytosol: DHAP + NADH → Glycerol 3-P + NAD⁺ (enzyme: cytosolic G3P dehydrogenase) - Arrow going DOWN through membrane: Glycerol 3-P enters mitochondria - In membrane/matrix: Glycerol 3-P + FAD → DHAP + FADH₂ (enzyme: mitochondrial G3P dehydrogenase) - DHAP arrow going back UP to cytosol - FADH₂ arrow going to "CoQ → ETC" with label "~1.5 ATP" - Badge: "ATP YIELD: 1.5 per NADH" RIGHT SIDE - "Malate-Aspartate Shuttle" (green/orange theme): - Label at top: "MALATE-ASPARTATE SHUTTLE" - Subtitle: "Efficient • More Steps • Heart, Liver & Kidney" - Same membrane division - In cytosol: OAA + NADH → Malate + NAD⁺ (cytosolic malate dehydrogenase) - Arrow DOWN: Malate enters matrix via malate-α-KG transporter - In matrix: Malate + NAD⁺ → OAA + NADH → Complex I → ETC - OAA + Glutamate → Aspartate + α-KG (aspartate aminotransferase) - Aspartate exits UP via glutamate-aspartate transporter - α-KG exits UP via malate-α-KG transporter - Aspartate + α-KG → OAA + Glutamate in cytosol (cycle restarts) - Badge: "ATP YIELD: 2.5 per NADH" CENTER DIVIDER - comparison table: Feature | G3P Shuttle | Malate-Asp Shuttle Tissue: Muscle/Brain | Heart/Liver/Kidney Carrier: DHAP/Glycerol-3P | Malate/Aspartate Electron acceptor: FAD | NAD⁺ ETC entry: CoQ | Complex I ATP yield: 1.5 | 2.5 Steps: Simple (2) | Complex (6) BOTTOM - bold text: "Both shuttles transfer cytosolic NADH electrons into the mitochondria — NADH itself cannot cross the inner membrane" Overall style: Clean white background, bold colored arrows, professional medical textbook style, well-organized, easy to read fonts, color-coded sections

Here's your comparison poster! It shows both shuttles side by side with:

Blue side - Glycerol 3-P shuttle with the simple 2-step cycle, FAD as the electron acceptor, and the 1.5 ATP yield
Green/orange side - Malate-aspartate shuttle with the 6-step cycle, NAD⁺ as the acceptor, and the 2.5 ATP yield
Center table - quick feature-by-feature comparison
Membrane clearly shown separating cytosol from the mitochondrial matrix

The key takeaway at the bottom ties it all together - both shuttles exist because NADH itself simply cannot cross the inner mitochondrial membrane.

Image is confusing

Running Command

mkdir -p /tmp/workspace/shuttle-poster && ls /tmp/workspace/shuttle-poster/

Writing File

~/shuttle-poster/poster.py

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
from matplotlib.patches import FancyArrowPatch, FancyBboxPatch
import matplotlib.patheffects as pe

fig = plt.figure(figsize=(20, 14))
fig.patch.set_facecolor('#F8F9FA')

# ── Title ──────────────────────────────────────────────────────────────────────
fig.text(0.5, 0.965, 'Mitochondrial Shuttle Systems', ha='center', va='top',
         fontsize=26, fontweight='bold', color='#1a1a2e')
fig.text(0.5, 0.940, 'How cytosolic NADH electrons cross the inner mitochondrial membrane',
         ha='center', va='top', fontsize=13, color='#555555', style='italic')

# ── Divider line ───────────────────────────────────────────────────────────────
fig.add_artist(plt.Line2D([0.03, 0.97], [0.925, 0.925], color='#cccccc', linewidth=1.5, transform=fig.transFigure))

# ═══════════════════════════════════════════════════════════════════════════════
# COLORS
# ═══════════════════════════════════════════════════════════════════════════════
BLUE      = '#1565C0'
BLUE_LITE = '#E3F2FD'
BLUE_MED  = '#90CAF9'
GREEN     = '#2E7D32'
GREEN_LIT = '#E8F5E9'
GREEN_MED = '#A5D6A7'
MEMB_CLR  = '#B0BEC5'
MEMB_TXT  = '#37474F'
BOX_RAD   = 0.012
ARROW_KW  = dict(arrowstyle='->', color='#333333', lw=2,
                 mutation_scale=18, connectionstyle='arc3,rad=0')

def box(ax, x, y, w, h, label, sublabel=None,
        fc='#E3F2FD', ec='#1565C0', fontsize=11, subfontsize=9):
    rect = FancyBboxPatch((x - w/2, y - h/2), w, h,
                          boxstyle=f'round,pad=0.01',
                          facecolor=fc, edgecolor=ec, linewidth=2, zorder=3)
    ax.add_patch(rect)
    ax.text(x, y + (0.018 if sublabel else 0), label,
            ha='center', va='center', fontsize=fontsize,
            fontweight='bold', color=ec, zorder=4)
    if sublabel:
        ax.text(x, y - 0.030, sublabel, ha='center', va='center',
                fontsize=subfontsize, color='#444444', zorder=4, style='italic')

def arrow(ax, x1, y1, x2, y2, color='#333333', label='', label_side='right'):
    ax.annotate('', xy=(x2, y2), xytext=(x1, y1),
                arrowprops=dict(arrowstyle='->', color=color, lw=2.2,
                                mutation_scale=18))
    if label:
        mx, my = (x1+x2)/2, (y1+y2)/2
        dx = 0.025 if label_side == 'right' else -0.025
        ax.text(mx + dx, my, label, ha='left' if label_side == 'right' else 'right',
                va='center', fontsize=8.5, color=color, style='italic')

def membrane_band(ax, y_top, y_bot, x_left=0.0, x_right=1.0):
    rect = mpatches.Rectangle((x_left, y_bot), x_right - x_left, y_top - y_bot,
                               facecolor=MEMB_CLR, alpha=0.35, zorder=1)
    ax.add_patch(rect)
    ax.axhline(y_top, color=MEMB_CLR, linewidth=2.5, zorder=2)
    ax.axhline(y_bot, color=MEMB_CLR, linewidth=2.5, zorder=2)

def zone_label(ax, x, y, text, color):
    ax.text(x, y, text, ha='center', va='center', fontsize=9,
            fontweight='bold', color=color,
            bbox=dict(fc='white', ec=color, alpha=0.85, boxstyle='round,pad=0.3'))

# ═══════════════════════════════════════════════════════════════════════════════
# LEFT PANEL — Glycerol 3-P Shuttle
# ═══════════════════════════════════════════════════════════════════════════════
ax1 = fig.add_axes([0.03, 0.09, 0.44, 0.83])
ax1.set_xlim(0, 1); ax1.set_ylim(0, 1)
ax1.axis('off')
ax1.set_facecolor(BLUE_LITE)

# Panel title
ax1.text(0.5, 0.965, 'GLYCEROL 3-PHOSPHATE SHUTTLE', ha='center', va='top',
         fontsize=15, fontweight='bold', color=BLUE)
ax1.text(0.5, 0.935, 'Skeletal Muscle  •  Brain', ha='center', va='top',
         fontsize=11, color=BLUE, style='italic')

# ATP badge
badge = FancyBboxPatch((0.32, 0.895), 0.36, 0.032,
                        boxstyle='round,pad=0.01', facecolor=BLUE, edgecolor=BLUE)
ax1.add_patch(badge)
ax1.text(0.50, 0.912, 'ATP YIELD:  ~1.5 per NADH', ha='center', va='center',
         fontsize=10.5, fontweight='bold', color='white')

# Zone labels
zone_label(ax1, 0.15, 0.80, 'CYTOSOL', BLUE)
zone_label(ax1, 0.15, 0.18, 'MATRIX', BLUE)

# Membrane
membrane_band(ax1, 0.535, 0.455)
ax1.text(0.85, 0.495, 'Inner\nMitochondrial\nMembrane', ha='center', va='center',
         fontsize=8, color=MEMB_TXT, fontweight='bold')

# ── CYTOSOL nodes ──
box(ax1, 0.30, 0.830, 0.22, 0.055, 'Glucose → Pyruvate',
    sublabel='(Glycolysis)', fc='white', ec=BLUE, fontsize=10)

box(ax1, 0.30, 0.730, 0.20, 0.055, 'NADH + H⁺',
    fc=BLUE_LITE, ec=BLUE, fontsize=11)

box(ax1, 0.70, 0.730, 0.20, 0.055, 'NAD⁺',
    fc='white', ec=BLUE, fontsize=11)

box(ax1, 0.30, 0.615, 0.24, 0.055, 'Glycerol 3-P',
    fc=BLUE_MED, ec=BLUE, fontsize=11)

box(ax1, 0.70, 0.615, 0.20, 0.055, 'DHAP',
    fc='white', ec=BLUE, fontsize=11)

# Cytosol arrows
arrow(ax1, 0.30, 0.803, 0.30, 0.758)               # Glucose → NADH
arrow(ax1, 0.30, 0.757, 0.30, 0.643)               # NADH → Glycerol 3-P
ax1.text(0.07, 0.700, 'Cytosolic\nG3P\nDehydrogenase',
         ha='center', va='center', fontsize=8.5, color=BLUE, style='italic')
arrow(ax1, 0.70, 0.643, 0.70, 0.757)               # DHAP → NAD+  (return)
arrow(ax1, 0.60, 0.730, 0.40, 0.730, color='#888888')  # NAD+ feeds back

# Cross-membrane arrows
arrow(ax1, 0.30, 0.588, 0.30, 0.477, color=BLUE, label='enters', label_side='left')
arrow(ax1, 0.70, 0.477, 0.70, 0.588, color='#888888', label='returns', label_side='right')

# ── MATRIX nodes ──
box(ax1, 0.30, 0.390, 0.24, 0.055, 'Glycerol 3-P',
    fc=BLUE_MED, ec=BLUE, fontsize=11)

box(ax1, 0.70, 0.390, 0.20, 0.055, 'DHAP',
    fc='white', ec=BLUE, fontsize=11)

box(ax1, 0.30, 0.270, 0.20, 0.055, 'FAD',
    fc='white', ec=BLUE, fontsize=11)

box(ax1, 0.70, 0.270, 0.22, 0.055, 'FADH₂',
    fc='#FFCC02', ec='#E65100', fontsize=11)

box(ax1, 0.50, 0.140, 0.34, 0.055, 'CoQ → ETC',
    sublabel='(bypasses Complex I)', fc='#FF8F00', ec='#E65100', fontsize=11)

ax1.text(0.07, 0.340, 'Mitochondrial\nG3P\nDehydrogenase',
         ha='center', va='center', fontsize=8.5, color=BLUE, style='italic')

arrow(ax1, 0.30, 0.363, 0.30, 0.298)               # G3P → FAD
arrow(ax1, 0.30, 0.298, 0.59, 0.298, color=BLUE)   # FAD → FADH2
arrow(ax1, 0.70, 0.363, 0.70, 0.298)               # G3P → DHAP
arrow(ax1, 0.59, 0.270, 0.70, 0.298, color='#888888')
arrow(ax1, 0.50, 0.243, 0.50, 0.168, color='#E65100', label='→ 1.5 ATP')

# ═══════════════════════════════════════════════════════════════════════════════
# RIGHT PANEL — Malate-Aspartate Shuttle
# ═══════════════════════════════════════════════════════════════════════════════
ax2 = fig.add_axes([0.52, 0.09, 0.45, 0.83])
ax2.set_xlim(0, 1); ax2.set_ylim(0, 1)
ax2.axis('off')
ax2.set_facecolor(GREEN_LIT)

# Panel title
ax2.text(0.5, 0.965, 'MALATE-ASPARTATE SHUTTLE', ha='center', va='top',
         fontsize=15, fontweight='bold', color=GREEN)
ax2.text(0.5, 0.935, 'Heart  •  Liver  •  Kidney', ha='center', va='top',
         fontsize=11, color=GREEN, style='italic')

# ATP badge
badge2 = FancyBboxPatch((0.32, 0.895), 0.36, 0.032,
                         boxstyle='round,pad=0.01', facecolor=GREEN, edgecolor=GREEN)
ax2.add_patch(badge2)
ax2.text(0.50, 0.912, 'ATP YIELD:  ~2.5 per NADH', ha='center', va='center',
         fontsize=10.5, fontweight='bold', color='white')

# Zone labels
zone_label(ax2, 0.15, 0.80, 'CYTOSOL', GREEN)
zone_label(ax2, 0.15, 0.18, 'MATRIX', GREEN)

# Membrane
membrane_band(ax2, 0.535, 0.455)
ax2.text(0.86, 0.495, 'Inner\nMitochondrial\nMembrane', ha='center', va='center',
         fontsize=8, color=MEMB_TXT, fontweight='bold')

# Transporter labels on membrane
ax2.text(0.28, 0.495, 'Malate/α-KG\ntransporter', ha='center', va='center',
         fontsize=7.5, color='#4A148C', fontweight='bold',
         bbox=dict(fc='#EDE7F6', ec='#4A148C', boxstyle='round,pad=0.2'))
ax2.text(0.68, 0.495, 'Glu/Asp\ntransporter', ha='center', va='center',
         fontsize=7.5, color='#BF360C', fontweight='bold',
         bbox=dict(fc='#FBE9E7', ec='#BF360C', boxstyle='round,pad=0.2'))

# ── CYTOSOL nodes ──
box(ax2, 0.50, 0.840, 0.22, 0.050, 'Glucose → Pyruvate',
    sublabel='(Glycolysis)', fc='white', ec=GREEN, fontsize=10)

box(ax2, 0.22, 0.745, 0.20, 0.050, 'OAA', fc='white', ec=GREEN, fontsize=11)
box(ax2, 0.50, 0.745, 0.20, 0.050, 'NADH', fc=GREEN_LIT, ec=GREEN, fontsize=11)
box(ax2, 0.78, 0.745, 0.20, 0.050, 'NAD⁺', fc='white', ec=GREEN, fontsize=11)

box(ax2, 0.22, 0.630, 0.20, 0.050, 'Malate', fc=GREEN_MED, ec=GREEN, fontsize=11)

box(ax2, 0.78, 0.630, 0.20, 0.050, 'Aspartate', fc='#FFCCBC', ec='#BF360C', fontsize=10)
box(ax2, 0.78, 0.560, 0.20, 0.050, 'α-KG', fc='#FFCCBC', ec='#BF360C', fontsize=10)

ax2.text(0.50, 0.690, 'Cytosolic malate\ndehydrogenase', ha='center', va='center',
         fontsize=8, color=GREEN, style='italic')
ax2.text(0.50, 0.600, 'Aspartate\naminotransferase\n(cytosolic)', ha='center',
         va='center', fontsize=7.5, color='#BF360C', style='italic')

# Cytosol arrows
arrow(ax2, 0.50, 0.815, 0.50, 0.770)               # Gluc → NADH
arrow(ax2, 0.40, 0.745, 0.32, 0.745)               # NADH → OAA side
arrow(ax2, 0.22, 0.720, 0.22, 0.655)               # OAA → Malate
arrow(ax2, 0.60, 0.745, 0.68, 0.745)               # NADH → NAD+
# OAA + Glu → Asp + α-KG  in cytosol (return cycle)
ax2.annotate('', xy=(0.78, 0.655), xytext=(0.68, 0.745),
             arrowprops=dict(arrowstyle='->', color='#BF360C', lw=1.8, mutation_scale=16,
                             connectionstyle='arc3,rad=-0.3'))

# Cross-membrane arrows
arrow(ax2, 0.22, 0.605, 0.22, 0.477, color='#4A148C', label='Malate in', label_side='left')
arrow(ax2, 0.68, 0.477, 0.68, 0.555, color='#BF360C', label='Asp out', label_side='right')
arrow(ax2, 0.33, 0.477, 0.33, 0.555, color='#4A148C', label='α-KG out', label_side='left')

# ── MATRIX nodes ──
box(ax2, 0.22, 0.390, 0.20, 0.050, 'Malate', fc=GREEN_MED, ec=GREEN, fontsize=11)
box(ax2, 0.50, 0.390, 0.20, 0.050, 'NAD⁺', fc='white', ec=GREEN, fontsize=11)

box(ax2, 0.22, 0.280, 0.20, 0.050, 'OAA', fc='white', ec=GREEN, fontsize=11)
box(ax2, 0.50, 0.280, 0.22, 0.050, 'NADH', fc='#C8E6C9', ec=GREEN, fontsize=12)

box(ax2, 0.78, 0.335, 0.20, 0.050, 'Aspartate', fc='#FFCCBC', ec='#BF360C', fontsize=10)
box(ax2, 0.78, 0.260, 0.20, 0.050, 'α-KG', fc='#FFCCBC', ec='#BF360C', fontsize=10)
box(ax2, 0.78, 0.185, 0.20, 0.050, 'Glutamate', fc='#FFCCBC', ec='#BF360C', fontsize=10)

box(ax2, 0.36, 0.155, 0.30, 0.050, 'Complex I → ETC',
    sublabel='(full NADH yield!)', fc='#388E3C', ec='#1B5E20', fontsize=11)

ax2.text(0.50, 0.340, 'Mitochondrial malate\ndehydrogenase', ha='center', va='center',
         fontsize=8, color=GREEN, style='italic')
ax2.text(0.78, 0.130, 'Aspartate\naminotransferase\n(matrix)', ha='center', va='center',
         fontsize=7.5, color='#BF360C', style='italic')

# Matrix arrows
arrow(ax2, 0.22, 0.365, 0.22, 0.305)               # Malate → OAA
arrow(ax2, 0.40, 0.390, 0.60, 0.390)               # pull NAD+
arrow(ax2, 0.40, 0.280, 0.39, 0.280)
arrow(ax2, 0.32, 0.280, 0.39, 0.280)
arrow(ax2, 0.40, 0.280, 0.61, 0.280, color=GREEN)  # OAA → NADH
arrow(ax2, 0.50, 0.255, 0.45, 0.180, color='#1B5E20', label='→ 2.5 ATP')
# Asp ↔ α-KG cycle in matrix
ax2.annotate('', xy=(0.78, 0.210), xytext=(0.78, 0.310),
             arrowprops=dict(arrowstyle='->', color='#BF360C', lw=1.8, mutation_scale=16))

# ── Cycle-back arrows (glutamate/aspartate from matrix → transporters) ──
arrow(ax2, 0.68, 0.335, 0.68, 0.477, color='#BF360C')  # Asp goes up to transporter
arrow(ax2, 0.33, 0.390, 0.33, 0.477, color='#4A148C')  # α-KG up

# ═══════════════════════════════════════════════════════════════════════════════
# BOTTOM COMPARISON TABLE
# ═══════════════════════════════════════════════════════════════════════════════
ax3 = fig.add_axes([0.03, 0.01, 0.94, 0.072])
ax3.set_xlim(0, 1); ax3.set_ylim(0, 1)
ax3.axis('off')
ax3.set_facecolor('#1a1a2e')

headers  = ['Feature', 'Glycerol 3-P Shuttle', 'Malate-Aspartate Shuttle']
row1     = ['Tissue',      'Skeletal Muscle, Brain',    'Heart, Liver, Kidney']
row2     = ['Electron carrier', 'DHAP ↔ Glycerol 3-P', 'OAA ↔ Malate + Asp/Glu']
row3     = ['Electron acceptor', 'FAD',                 'NAD⁺']
row4     = ['ETC entry',   'CoQ  (skips Complex I)',     'Complex I  (full chain)']
row5     = ['ATP / NADH',  '~1.5 ATP',                  '~2.5 ATP']

col_x    = [0.08, 0.38, 0.72]
col_clrs = ['#CFD8DC', BLUE_MED, GREEN_MED]

for ci, (cx, txt, cc) in enumerate(zip(col_x, headers, ['#ECEFF1', BLUE_MED, GREEN_MED])):
    ax3.text(cx, 0.82, txt, ha='center', va='center', fontsize=10,
             fontweight='bold', color='#1a1a2e',
             bbox=dict(fc=cc, ec='none', boxstyle='round,pad=0.3', alpha=0.95))

for ri, row in enumerate([row1, row2, row3, row4, row5]):
    y = 0.62 - ri * 0.145
    clrs = ['#ECEFF1', '#E3F2FD', '#E8F5E9']
    for ci, (cx, val) in enumerate(zip(col_x, row)):
        ax3.text(cx, y, val, ha='center', va='center',
                 fontsize=9, color='#1a1a2e',
                 bbox=dict(fc=clrs[ci], ec='none', boxstyle='round,pad=0.2', alpha=0.80))

plt.savefig('/tmp/workspace/shuttle-poster/mitochondrial_shuttles.png',
            dpi=150, bbox_inches='tight', facecolor=fig.get_facecolor())
print("Saved.")

Running Command

cd /tmp/workspace/shuttle-poster && python poster.py 2>&1

Reading File

Here's your clean, programmatic comparison poster:

mitochondrial shuttles

Image · PNG

What's in it:

Left panel (blue) - Glycerol 3-P shuttle: simple 2-node cycle, DHAP ↔ Glycerol 3-P as carriers, electrons land on FAD → CoQ, yields 1.5 ATP
Right panel (green/orange) - Malate-aspartate shuttle: the 6-step cycle with malate, OAA, aspartate, glutamate, α-KG, and the two membrane transporters clearly labeled, electrons enter at Complex I, yields 2.5 ATP
Grey band = inner mitochondrial membrane, separating cytosol (top) from matrix (bottom) in each panel
Bottom table = side-by-side feature comparison

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