Open AccessGolgi galactosyltransferase contains serine‐linked phosphate
Author(s) -
STROUS Ger J.,
KERKHOF Peter,
FALLON Robert J.,
SCHWARTZ Alan L.
Publication year - 1987
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1987.tb13613.x
Subject(s) - galactosyltransferase , serine , phosphorylation , biochemistry , enzyme , phosphate , golgi apparatus , methionine , polyacrylamide gel electrophoresis , chemistry , gel electrophoresis , biology , microbiology and biotechnology , amino acid , cell
In HeLa and HepG2 cells the Golgi complex enzyme galactosyltransferase became phosphorylated following incubation with 32 P i . Analysis on sodium dodecyl sulphate/polyacrylamide gel electrophoresis revealed incorporation of 32 P into the mature 54‐kDa form. This phosphorylation was independent of protein synthesis. Serine was identified as the sole phosphorylated amino acid; no radioactive phosphate was detected on N‐linked oligosaccharide. The phosphate‐labelled galactosyltransferase has the same turnover as [ 35 S]methionine‐labelled polypeptides ( t 1/2 = 20 h). Soluble enzyme, released by the cells, contained very little phosphate relative to that which remained cell‐associated. Charge heterogeneity arising from phosphorylation contributes in part to the heterodispersed appearance of the enzyme on two‐dimensional gels, as the degree of radioactive phosphate differs among the different iso‐enzymes.