Isolation and sequence determination of two pyridoxal 5'-phosphate-labeled thermolysin peptides from pig muscle phosphoglucose isomerase.

Pig muscle phosphoglucose isomerase modified with pyridoxal 5'-phosphate under conditions that cause at least 90% inactivation of its catalytic activity was found to incorporate about 1.5 eq of pyridoxal 5'-phosphate per subunit. After digestion with thermolysin, two pyridoxal 5'-phosphate-containing peptides were isolated and their amino acid sequences were determined to be Leu-Gly-pyridoxyl-Lys-Gln and Ile-Ala-Ser-pyridoxyl-Lys-Thr.