Glyceraldehyde-3-phosphate dehydrogenase

The Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) enzyme serves two functions in glycolytic pathway. First the enzyme transfers a hydrogen (H-) from glyceraldehyde phosphate (Gly3P) to the oxidizing agent Nicotinamide Adenine Dinucleotide (NAD+) to form NADH. Next it adds a phosphate (P) from the cytosol to the oxidized Gly3P to form 1, 3-bisphosphoglycerate.

Chemical equation

$NAD + Gly3P + Pi \rightleftharpoons 1,3BPG + NADH$

Rate equation

Ordererd Ter-Bi reversible Michaelis-Menten equation for non-interacting substrates.

$v = \frac{ V_{mf}\frac{[NAD][Gly3P][Pi]}{K_{NAD}K_{Gly3P}K_{Pi}} - V_{mr} \frac{[1,3BPG][NADH]}{K_{1,3BPG}K_{NADH}} }{1 + \frac{[NAD]}{K_{NAD}} + \frac{[NAD][Gly3P]}{K_{NAD}K_{Gly3P}} + \frac{[NAD][Gly3P][Pi]}{K_{NAD}K_{Gly3P}K_{Pi}} + \frac{[1,3BPG][NADH]}{K_{1,3BPG}K_{NADH}} + +\frac{[NADH]}{K_{NADH}} }$

Parameters

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	0.58	$mM \times min^{-1}$	HeLa cell line
$V_{mr}$	0.72	$mM \times min^{-1}$
$Km_{Gly3P}$	0.19	mM
$Km_{1,3BPG}$	0.022	mM
$Km_{NAD+}$	0.09	mM
$Km_{NADH}$	0.01	mM
$Km_{Pi}$	29	mM

Parameters with uncertainty

• 4 values of $Km_{NADH}$ have been collected from Lambeir et. al. (1991) for different organisms. $Km_{NADH} = 0.007$ for Trypanosoma brucei, $Km_{NADH} = 0.01$ for Homo sapiens, $Km_{NADH} = 0.012$ for Geobacillus stearothermophilus and $Km_{NADH} = 0.012$ for Oryctolagus cuniculus. Calculating mean and std. dev. from these 4 values gives Failed to parse (Cannot store math image on filesystem.): Km_{NADH} = 0.01025 \pm 0.004063

Parameter	Value	Units	Organism	Remarks
$V_{mf}$	$2 \pm 0.74 (5)$	$mM \times min^{-1}$	HeLa cell line
$V_{mr}$	$2.5 \pm 0.8$ (5)	$mM \times min^{-1}$
$Km_{Gly3P}$	0.19	mM
$Km_{1,3BPG}$	0.022	mM
$Km_{NAD+}$	0.09	mM
$Km_{NADH}$	Failed to parse (Cannot store math image on filesystem.): 0.01025 \pm 0.004063	mM
$Km_{Pi}$	29	mM