Terminal residues of hog pancreatic amylase

Studies on the identification of the terminal residues in protease-free hog pancreatic alpha-amylase, prepared by glycogen precipitation, demonstrated the absence of free amino terminals when four different chemical procedures were used. These methods were based on reaction with fluorodinitrobenzene, trinitrobenzenesulfonic acid, dansyl chloride, and cyanate. In the search for the presence of a possible alpha-N-blocking group, an acetyl group was detected as acetic acid dinitrophenyl hydrazide after hydrazinolysis and dinitrophenylation. Quantitation of acetyl groups by a gas chromatographic or a specific enzymatic method yielded 0.7 mol of acetyl group per 51,000 g of protein. Other acyl groups, such as formyl or propionyl, were not found. Leucine was shown to be the carboxyl terminal residue by hydrazinolysis or by carboxypeptidase A digestion of acid denatured amylase. With either procedure, 0.8 mol of carboxyl terminal leucine was found per 51,000 g of protein. These findings are consistent with the proposal that hog pancreatic alpha-amylase is composed of a single, alpha-N-acetylated chain of molecular weight 50,000. Claims of other investigators for subunit and multichain structures for this enzyme are discussed in view of these end group data.