Physical properties of gamma-glutamyltransferase in human serum

Using gel chromatography on Sephacryl S300 we have separated serum gamma-glutamyltransferase into three fractions with estimated relative molecular masses of (a) greater than 1000 000, (b) 250 000-500 000 and (c) about 120 000. Similarly, serum leucine aminopeptidase has been separated into three fractions. We have studied, particularly, the gamma-glutamyltransferase fraction of intermediate relative molecular mass (250 000-500 000) in serum from patients with a number of liver diseases. We have shown, both by polyanion and immuno-precipitation, that it consists significantly of a complex between gamma-glutamyltransferase and high density lipoprotein. The physical properties of this fraction, namely its mass and charge, can be altered by incubating serum with either bile or bile salts.