Multiple Forms of Human γ-Glutamyltransferase

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Abstract
Several forms of .gamma.-glutamyltransferase were prepared from human liver, bile and serum by size-dependent means, were subjected to digestions with trypsin, neuraminidase and phospholipases, extraction with deoxycholate and organic solvents, and freezing and thawing, to attempt the elucidation of 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 < 20,000 MW, 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.