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

We report that ATP enhances the activity of galactosyltransferase-I, which synthesizes the linkage region between glycosaminoglycan chains and the cor e proteins of proteoglycans. The enzyme activity in cell-free fractions pre pared from cultured human skin fibroblasts was measured by high-performance liquid chromatographic detection of galactosyl-xylosyl-(4-methylumbellifer one) produced from 4-methylumbelliferyl- beta -D-xyloside used as an accept or. ATP at 2 mM increased the enzyme activity by about 60% in the 110 x g s upernatant of the cell homogenate, but not in the supernatant or precipitat e fractions obtained by 100 000 x g centrifugation. When both fractions (th e 100 000 x g supernatant and precipitate) were mixed, the additional ATP i ncreased the enzyme activity. This increase was canceled by heat treatment or trypsin digestion of the 100 000 x g supernatant. In addition, the 100 0 00 x g precipitate, which was prepared from the 110 x g supernatant preincu bated with ATP, exhibited increased activity, and this increase was abolish ed by alkaline phosphatase treatment. These results suggest that a protein kinase in the 100 000 x g supernatant activates galactosyltransferase-I act ivity.