Multiple forms of human gamma-glutamyltransferase: modification and possible structures of different molecular weight...

Several forms of gamma-glutamyltransferase have been prepared from human liver, bile and serum by size-dependent means, and have been subjected to digestions with trypsin, neuraminidase and phospholipases, extraction with deoxycholate and organic solvents, and freezing and thawing, to attempt to elucidate their nature and interrelationships. In general, these treatments alter the size and charge of the original fractions, producing in some cases resemblances between originally distinct fractions. All the forms appear to contain a catalytically active component of less than 20,000 molecular weight, which may be the small subunit of a common enzyme molecule. The observations are consistent with the view that multiple forms of gamma-glutamyltransferase in human serum and bile arise by various modifications of a single type of enzyme.