The binding of decomposition products of UDP-galactose to the microsomes and polyribosomes isolated from rat liver.

UDP-D-[U-14C]galactose is decomposed to [U-14C]galactose-1-phosphate and [U-14C]galactose by rat liver microsomal and crude polyribosomal fractions, under conditions commonly used to assay of glycosyltransferase activities. UDP-D-[U-14C]galactose, at neutral pH, is also chemically degraded to the [U-14C]galactose-1,2-cyclic phosphate. The 1,2-cyclic phosphate derivative of galactose also exists in the commercial UDP-D-[U-14C]galactose. It is a very important finding that products of the UDP-D-[U-14C]galactose decomposition are tightly, although nonenzymatically, bound to tested subcellular fractions and may create a false impression of protein glycosylation. The application of controls containing all radioactive substances present in suitable samples is recommended in order to avoid incorrect interpretations of the results.