JBC, Vol. 251, Issue 2, 285-291, Jan, 1976
Biosynthesis of chondroitin sulfate. Role of phospholipids in the activity of UDP-D-galactose: D-xylose galactosyltransferase
N. B. Schwartz
The role of phospholipids in the activity of UDP-D-galactose: D-xylose
galactosyltransferase (galactosyltransferase I) from embryonic chick
cartilage was investigated. Phospholipase C treatment of particulate
galactosyltransferase I caused inactivation of this enzyme to the extent of
60 to 70% as well as hydrolysis of 75 to 80% of the membrane phospholipids.
Addition of phospholipid restored activity to nearly control levels. The
order of effectiveness of various phopholipids in reactivating
phospholipase C-treated galactosyltransferase I was as follows:
lysophosphatidylcholine, lysophosphatidylethanolamine,
phosphatidylethanolamine, phosphatidylcholine. The effect of phospholipase
A on galactosyltransferase I activity was also examined and was found to be
concentration-dependent. At concentrations less than 10 mug/mg of pellet
protein, phospholipase A slightly activated galactosyltransferase I.
whereas at higher concentrations it inhibited the activity in a manner
similar to phospholipase C. Galactosyltransferase I was activated
moderately and also solubilized by treatment with Nonidet P-40 in the
presence of 0.5 M KCl. Following solubilization and purification by gel
filtration and affinity chromatography, galactosyltransferase I could be
inactivated by detergent removal by dialysis and subsequently reactivated
by addition of detergent. Neither phospholipase C treatment nor exogenous
phospholipid had any significant effect on three of the other chondroitin
sulfate glycosyltransferases (UDP-D-xylose: core protein
xylosyltransferase, UDP-D-glucuronic acid:3-O-beta-D-galactosyl-D-galactose
glucuronosyltransferase, and
UDP-N-acetyl-D-galactosamine:(BlcUA-GalNAc-4-sulfate)j
N-acetylgalactosaminyltransferase). On lipid analysis by thin layer
chromatography, phosphatidylcholine and phosphatidylethanolamine were found
to be the major phospholipids of particulate and solubilized
glycosyltransferase preparations from embryonic chick cartilage, while
lysopholipids of particulate and solubilized glycosyltransferase
preparations from embryonic chick cartilage, while lysophosphatidylcholine
and lysophosphatidylethanolamine were barely detectable components. The
concentration of these specific phospholipids was diminished greatly
following phospholipase C treatment.