Stimulation of collagen galactosyltransferase and glucosyltransferase activities by lysophosphatidylcholine

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Abstract
Lysophosphatidylcholine stimulated the activities of collagen galactosyl- and glucosyl-transferases in chick-embryo extract and its particulate fractions in vitro, but essentially no stimulation was noted in the high-speed supernatant, where the enzymes were soluble and membrane-free. The stimulatory effect of lysophosphatidylcholine was masked by 0.1% Triton X-100. In kinetic experiments, lysophosphatidylcholine raised the maximum velocities with respect to the substrates and co-substrates but no changes were observed in the apparent Km values. Phospholipase A preincubation of the chick-embryo extract resulted in stimulation of both transferase activities, probably by generating lysophosphatides from endogenous phospholipids. No stimulation by lysophosphatidylcholine was found when tested with 5000-fold-purified glucosyltransferase. Collagen glycosyltransferase apparently must be associated with the membrane structures of the cell in order to be stimulated by lysophosphatidylcholine. Lysophosphatidylcholine could have some regulatory significance in vivo, since its concentration in the cell was comparable with that which produced marked stimulation in vitro.

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