Methylenetetrahydrofolate dehydrogenase – methenyltetrahydrofolate cyclohydrolase – formyltetrahydrofolate synthetase from porcine liver Location of the activities in two domains of the multifunctional polypeptide

Abstract

Chymotryptic cleavage of the trifunctional protein methylenetetrahydrofolate dehydrogenase – methenyltetrahydrofolate cyclohydrolase – formyltetrahydrofolate synthetase from pig liver yields a fragment of two-thirds the original polypeptide that retains only synthetase activity. A smaller polypeptide corresponding to about one-third of the original polypeptide was shown earlier to retain dehydrogenase–cyclohydrolase activity. On immunodiffusion, the synthetase fragment cross-reacts and shows partial identity with antibodies raised against the uncleaved enzyme but shows nonidentity with the dehydrogenase–cyclohydrolase fragment, suggesting that the two fragments are derived from different regions of the polypeptide. Amino-terminal analysis of the peptides and uncleaved enzyme indicate that the dehydrogenase–cyclohydrolase activities are located at the amino-terminal region and the synthetase near the carboxyl-terminal portion of the polypeptide.