Purification and properties of two succinate semialdehyde dehydrogenases from human brain

In human brain there are two major isoenzymes of succinate semialdehyde dehydrogenase (succinate-semialdehyde: NAD+ oxidoreductase, EC 1.2.1.24). They are composed of two apparently identical subunits with a molecular weight of 69 000. The Km (limits) for their substrates NAD+ and succinate semialdehyde are 1.6.10(-5) M and 3.7.10(-6) M, respectively, for one enzyme, and 1.85.10(-5) M and 2.10(-6) M, respectively, for the other. These values, and other kinetic data obtained from the two enzymes are not very different. However the enzymes differ in the following respects: their behavior on ion exchange and 5'-AMP affinity columns, their isoelectric points, their tryptic fingerprints and in their amino acid compositions.