KINETIC-BEHAVIOR AND PROPERTIES OF ALDEHYDE DEHYDROGENASE FROM RAT TESTIS MITOCHONDRIA - EFFECT OF MG2+ IONS

1. Mitochondrial aldehyde dehydrogenase is purified to near homogeneity by hydroxylapatite-, affinity- and hydrophobic interaction-chromatography. 2. The enzyme is an oligomeric protein and its molecular weight, as determined by gel-filtration, is 117,000 +/- 5000. 3. Active only in the presence of exogenous sulphhydryl compounds and NAD+-dependent, aldehyde dehydrogenase works optimally with linear-chain aliphatic aldehydes and is practically inactive with benzaldehyde. The pH-optimum is at about pH 8.5. 4. K(m)-Values for aliphatic aldehydes (C2-C6) range between 0. 17 and 0. 32-mu-M. The K(m) for NAD+ increases from 16-mu-M with acetaldehyde to 71-mu-M with capronaldehyde. 5. Millimolar concentrations of Mg2+ promote high increases of both V and K(m) for NAD+. At the same time, saturation curves with C4-C6 aldehydes can be simulated with a substrate inhibition model. 6. Inhibition by NADH is competitive: with capronaldehyde, the inhibition constant for NADH is 52-mu-M in the absence of Mg2+ and 14-mu-M in the presence of 4 mM Mg2+; with acetaldehyde, the inhibition constant is about three times higher (36 and 159-mu-M, respectively).