MOLECULAR AND CATALYTIC PROPERTIES OF ALDOLASE C

The catalytic, physical, and immunochemical properties of aldolase C are presented and compared with the corresponding properties of aldolases A and B. The three enzymes have different fructose 1,6-diphosphate: fructose 1-phosphate ratios (A = 50, B = 1, and C = 10), Michaelis constants for fructose 1-phosphate (A = 10-2 M, B = 3 X 10-4 m, C = 4 X 10-3 m), and specific fructose 1,6-diphosphate cleavage activites (A = 2900, B = 250, and C = 1000) and are inhibited to different extents by treatment with carboxypeptidase. They have similar Michaelis constants for fructose 1,6-diphosphate (1-3 X 10-6 m), similar catalytic properties after carboxypeptidase treatment, and nearly identical pH profiles for the fructose 1,6-diphosphate and fructose 1-phosphate cleavage reactions. The enzymes have different amino acid compositions and different primary structures as demonstrated by peptide mapping. In addition, they are immunochemically distinct with no cross-reactions observed among the three proteins. The data obtained suggest that aldolase A, B, and C are three distinct proteins which are structurally closely related and functionally distinct but homologous. © 1969, American Chemical Society. All rights reserved.