Defects of glycosyltransferase activities in human fibroblasts of Pk and p blood group phenotypes.

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Abstract
Human fibroblasts of the rare Pk phenotype lack globoside, which was identified as the blood group P antigen. Also, p cells possess neither globoside nor trihexosyl ceramide, which was identified as Pk antigen. These glycosphingolipid patterns are most likely caused by inherited preferential biosynthetic pathways in the abnormal phenotypes rather than by excess catabolism of the antigens. The fibroblasts of Pk phenotype lack .beta.-N-acetyl-galactosaminyltransferase (globoside synthetase; UDP-N-acetylgalactosamine:trihexosylceramide .beta.-N-acetylgalactosaminyltransferase; EC 2.4.1.79) activity, and those of p are deficient in .alpha.-galactosyltransferase (trihexosylceramide synthetase; UDP galactose:lactosylceramide .alpha.-galactosyltransferase) and possibly also in globoside synthetase. The diminished globoside synthetase activity in p cells is not caused by the defect in the gene coding for this enzyme. It appears to be caused by a failure in gene expression because 1/3 of Pk .times. p hybrids became able to express P antigenicity with a time lag of 3-4 days after cell fusion.