phosphorus-radioisotopes and fructose-1-6-diphosphate

Minimum values for the content of covalent intermediates in the equilibria of muscle aldolase with its cleavable substrates have been determined by acid denaturation/precipitation. Ribulose 1,5-bisphosphate, a nonsubstrate that binds well to aldolase in the native state, does not form a covalent complex that is acid precipitable. The insoluble protein complexes with substrates fructose 1,6-bisphosphate and sedoheptulose 1,7-bisphosphate, representing approximately 50% and approximately 60% of total bound substrate, are much more stable in acid and alkali than that with substrate 5-deoxyfructose 1,6-bisphosphate, suggesting that they have the form of protein-bound N-glycosides. Whether such complexes exist on the enzyme in the native state in addition to being formed subsequent to denaturation is unresolved. Both the acid-precipitable and nonprecipitable forms of fructose 1,6-bisphosphate are converted to triose phosphate products at the same rate, providing no kinetic evidence for a pool that is not on the main reaction path. Total fructose 1,6-bisphosphate liganded to enzyme returns to the free solution about 9 times for each net cleavage reaction. It is still not clear whether this is limited by the cleavage step or by release of glyceraldehyde phosphate.

Topics: Animals; Drug Stability; Fructose-Bisphosphate Aldolase; Fructosediphosphates; Glyceraldehyde 3-Phosphate; Glycosides; Hexosediphosphates; Hydrogen-Ion Concentration; Kinetics; Muscles; Phosphorus Radioisotopes; Protein Binding; Protein Denaturation; Rabbits; Substrate Specificity