FRUCTOSE-1,6-BISPHOSPHATE ALDOLASE FROM RABBIT LIVER - REACTION-MECHANISM AND PHYSIOLOGICAL-FUNCTION

Liver and muscle aldolase display similar reaction mechanisms. Both the enzymes, by reacting with dihydroxyacetone phosphate, form an acid‐labile intermediate which is in rapid equilibrium with an eneamine intermediate. Differences are found in the equilibrium concentration of the acid‐labile intermediate, which represents approximately 25% of the total intermediates in the liver (this paper) and 60% in the muscle enzyme [E. Grazi and G. Trombetta, Biochem. J. 175, 361 (1978)] and in the rate of formation of the eneamine intermediate which is much slower in the liver enzyme. Furthermore, with liver aldolase, the rate by which the C‐3H bond of dihydroxyacetone phosphate is cleaved is increased by 60 times in the presence of glyceraldehyde 3‐phosphate. This, mechanistically, indicates that glyceraldehyde 3‐phosphate is bound to the enzyme before the formation of the eneamine from dihydroxyacetone phosphate, and, physiologically, that in liver aldolase the gluconeogenetic activity is favoured over the glycolytic activity. Copyright © 1979, Wiley Blackwell. All rights reserved