On the Mechanism of Formation of a Partially Active Aldolase by Tryptic Digestion

The limited proteolysis of a fully active mercury derivative of rabbit muscle aldolase affects all four subunits of the enzyme, but not in a uniform way. At least four out of the nine peptides liberated are cleaved off from only two subunits. The specific activity of the product (aldolase‐T) is 50% of that of the native enzyme. The combined kinetic and peptide analytical study of aldolase‐T formation has shown that the diminished activity is the consequence of the splitting off of a particular tyrosine‐containing peptide from all four subunits of aldolase, and of the cleavage of a peptide bond in the vicinity of residue Cys‐341 in only two subunits. The data presented, together with the results of the polyacrylamide gel electrophoresis of aldolase‐T in the absence and presence of sodium dodecylsulfate, support the idea that the structure of oligomeric aldolase is of type AABB. Large segments of one kind of the subunits can be split off without affecting the tetrameric structure. A tentative sequence of the C‐terminal 60 amino acids of aldolase is also presented.