PRIMARY STRUCTURE OF PYRIDOXAL PHOSPHATE BINDING SITE IN MITOCHONDRIAL AND EXTRAMITOCHONDRIAL ASPARTATE AMINOTRANSFERASES FROM PIG HEART MUSCLE . CHYMOTRYPTIC PEPTIDES

For a comparison of the primary structures of the coenzyme binding sites in aspartate aminotransferases from the mitochondrial and extramitochondrial fractions of pig heart muscle, phosphopyridoxyl peptides were isolated from the chymotryptic digests of these two enzymes after borohydride reduction followed by carboxymethylation. The peptides containing the reduced coenzyme were then identified by their fluorescence characteristics. A single phosphopyridoxyl peptide was obtained from the extramitochondrial enzyme and its amino acid sequence was determined as Ser-(ϵ-phosphopyridoxyl)- Lys-Asn-Phe. Several pyridoxyl peptides were obtained from the mitochondrial enzyme. Some of them presumably resulted from side splits of a typical peptide, or from the oxidation of methionine to its sulfoxide during isolation procedures. The sequence, Ala-(ϵ-phosphopyridoxyl)-Lys-Asn-Met, was assigned to one of these typical peptides. © 1969, American Chemical Society. All rights reserved.