SUBUNIT STRUCTURE OF FRUCTOSE DIPHOSPHATE ALDOLASE FROM SPINACH LEAF

The subunit structure of spinach leaf fructose diphosphate aldolase has been examined by chemical and physical methods. In confirmation of previous results, the molecular weight of the native enzyme was found to be 120,000. The molecular weight of subunits obtained by treatment with maleic anhydride was 28,000-30,000, indicating a structure containing four subunits. Tyrosine appeared to be the amino acid in the C-terminal position. However, the quantity of tyrosine released by digestion with carboxypeptidase A varied from preparation to preparation, and was correlated with the specific activity of the preparation. The maximum number of tyrosines released was approximately 3 per mole of enzyme. The results suggest that specific modification or loss of C-terminal tyrosines had occurred during the isolation of the enzyme. Upon treatment with carboxypeptidase, one of the C-terminal tyrosine residues was released rapidly, while the other two were more resistant. Loss of catalytic activity was associated with the release of the sensitive tyrosine residue. © 1969.