TUMOR-TISSUE IS A SOURCE OF GAMMA-GLUTAMYL-TRANSPEPTIDASE SIALOFORM IN THE SERA OF MELANOMA-BEARING MICE

The total serum activity of gamma-glutamyl transpeptidase (GGT) was sh own to increase with the growth of transplantable B16 and S91 melanoma s in inbred mice. In an effort to define the source of the GGT shed in to the bloodstream the physicochemical characteristics of the partiall y purified GGT isoforms from liver, serum and B16 melanoma were compar ed. The molecular weights of the serum and melanoma isoforms were iden tical (86 kDa) and differed from that of the liver isoform (69 kDa). I n polyacrylamide gel electrophoresis the serum and melanoma isoforms h ad a similar mobility which exceeded that of the liver enzyme. Treatme nt of the enzyme preparations with neuraminidase removed the differenc es in the electrophoretic mobility of the three GGT isoforms studied. On ion exchange chromatography on a DEAE-Spheron 300 LC column the mel anoma and serum isoforms had an affinity to the sorbent unlike the liv er isoform. Our observations suggest that melanoma cells express a sia loform of GGT which is responsible for an increase in the total GGT se rum activity. Biochemical and histochemical analyses did not reveal an y increase in liver GGT production associated with melanoma developmen t. Detection of the GGT isoform of tumour origin in sera ranks GGT amo ng the specific melanoma markers. (C) 1998 Rapid Science Ltd.