Effects of ATP on regulation of galactosyltransferase-I activity responsible for synthesis of the linkage region between the core protein and glycosaminoglycan chains of proteoglycans

Abstract

We report that ATP enhances the activity of galactosyltransferase-I, which synthesizes the linkage region between glycosaminoglycan chains and the core proteins of proteoglycans. The enzyme activity in cell-free fractions prepared from cultured human skin fibroblasts was measured by high-performance liquid chromatographic detection of galactosyl-xylosyl-(4-methylumbelliferone) produced from 4-methylumbelliferyl-β-D-xyloside used as an acceptor. ATP at 2 mM increased the enzyme activity by about 60% in the 110 × g supernatant of the cell homogenate, but not in the supernatant or precipitate fractions obtained by 100 000 × g centrifugation. When both fractions (the 100 000 × g supernatant and precipitate) were mixed, the additional ATP increased the enzyme activity. This increase was canceled by heat treatment or trypsin digestion of the 100 000 × g supernatant. In addition, the 100 000 × g precipitate, which was prepared from the 110 × g supernatant preincubated with ATP, exhibited increased activity, and this increase was abolished by alkaline phosphatase treatment. These results suggest that a protein kinase in the 100 000 × g supernatant activates galactosyltransferase-I activity.Key words: ATP, enzyme activator, galactosyltransferase-I, proteoglycan linkage region.