A COMPARATIVE STUDY OF STRUCTURE OF MUSCLE FRUCTOSE 1,6-DIPHOSPHATE ALDOLASES

The primary structures of fructose diphosphate aldolases from the skeletal muscle of rabbit, pig, ox and sturgeon have been compared by means of zone electrophoresis, amino acid and N‐terminal analysis, peptide mapping and cyanogen bromide cleavage. The S‐carboxymethylated mammalian enzymes give two bands on polyacrylamide gel electrophoresis, under conditions where the S‐carboxymethylated sturgeon enzyme gives only one. The two bands usually stain unequally with the rabbit enzyme, whereas with the ox and pig enzymes a more equal intensity is observed. The mammalian enzymes are highly homologous by the criteria used, and it seems likely that the sturgeon enzyme will be fairly closely alike. In this degree of homology, the aldolases resemble the glyceraldehyde 3‐phosphate dehydrogenases from various sources, suggesting that such homology may be a common feature of glycolytic enzymes. Despite the occurrence of two bands in gel electrophoresis of the mammalian enzymes, it is clear that there cannot be substantial sequence differences between the subunit peptide chains of a given aldolase. Such differences, if they exist, must be relatively few in number. Other explanations, such as chemical modification of some of the chains, may account for the observed electrophoretic behaviour in the mammalian enzymes. The ox enzyme contains one additonal cysteine residue per subunit compared with the other mammalian enzymes. This change has been located in the primary structure and since the cysteine residue is reactive in the native ox enzyme, it may provide a useful site for attachment of heavy atoms in X‐ray crystallographic studies. Copyright © 1969, Wiley Blackwell. All rights reserved