The action of cytoplasmic aldehyde dehydrogenase on methyl p-nitrophenyl carbonate and p-nitrophenyl dimethylcarbamate.
Cytoplasmic aldehyde dehydrogenase catalyses the hydrolysis of methyl p-nitrophenyl (PNP) carbonate at an appreciable rate that is markedly stimualted by NAD+ or NADH. The nuleotides accelerate the rate-limiting hydrolysis of the acyl-enzyme intermediate while slowing the observed burst of p-nitrophenoxide production. With PNP dimethylcarbamate the enzyme catalyses the slow release of approx. 1 molecule of p-nitrophenoxide per tetrameric enzyme molecule; during the reaction the enzyme becomes effectively inactivated, as the rate of hydrolysis of the acyl-enzyme is virtually zero. The presence of NAD+, NADH, propionaldehyde, chloral hydrate, diethylstilboestrol or disulfiram slows the reaction of enzyme with PNP dimethylcarbamate. The reaction appears to be dependent on a group of pKa 7.6, possibly a cysteine residue. The effect of PNP dimethylcarbamate on the dehydrogenase activity of the enzyme is consistent with there being a single type of active site for the enzyme's dehydrogenase and esterase activities. Steric and electronic factors that govern reaction of the enzyme with PNP substrates are discussed.
Kitson
T M
TM
Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand.
D000444:Aldehyde Dehydrogenase / Q000378:metabolism*; D000818:Animals; D002219:Carbamates / Q000378:metabolism*; D002254:Carbonates / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology; D006868:Hydrolysis; D008099:Liver / Q000201:enzymology; D009243:NAD / Q000378:metabolism; D012756:Sheep
D002219:Carbamates; D002254:Carbonates; D009243:NAD; C008474:methyl-4-nitrophenylcarbonate; C054209:2-nitrophenyl dimethylcarbamate; D000444:Aldehyde Dehydrogenase