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I Melezínek

Publications and source records attributed to I Melezínek.

4 recordsLinked to original sources
PubMed1998

Tumour 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 shown to increase with the growth of transplantable B16 and S91 melanomas in inbred mice. In an effort to define the source of the GGT shed into the bloodstream the physicochemical characteristics of the partially purified GGT isoforms from liver, serum and B16 melanoma were compared. The molecular weights of the serum and melanoma isoforms were identical (86 kDa) and differed from that of the liver isoform (69 kDa). In polyacrylamide gel electrophoresis the serum and melanoma isoforms had a similar mobility which exceeded that of the liver enzyme. Treatment of the enzyme preparations with neuraminidase removed the differences in the electrophoretic mobility of the three GGT isoforms studied. On ion exchange chromatography on a DEAE-Spheron 300 LC column the melanoma and serum isoforms had an affinity to the sorbent unlike the liver isoform. Our observations suggest that melanoma cells express a sialoform of GGT which is responsible for an increase in the total GGT serum activity. Biochemical and histochemical analyses did not reveal any increase in liver GGT production associated with melanoma development. Detection of the GGT isoform of tumour origin in sera ranks GGT among the specific melanoma markers.

Animals↗
PubMed1986

Interference of melanin in protein determination.

Using several assay methods, synthetic eumelanin prepared by autooxidation of L-beta-(3,4-dihydroxyphenyl)alanine and a natural melanin isolated from dog hair melanosomes were tested in model experiments to assess their possible interference in protein determination. The degree of interference was assessed by comparing the data obtained with the melanin samples with those derived from measurements of bovine serum albumin. In the common biuret and Lowry methods melanin interferes by falsely increasing the values obtained; the addition of Folin reagent only after melanin removal, as suggested by Doezema, decreased but did not eliminate melanin interference. Methods working at acid pH such as those according to Salo and Honkavaara with Ponceau S or Sedmak and Grossberg or Spector using Coomassie blue G-250 proved much better. Although melanins adsorbed a small amount of dye from the reaction systems in these procedures, their sensitivity to proteins makes the melanin interference negligible. Such procedures can therefore be recommended for protein determination in the presence of melanin.

False Positive Reactions↗