The Alkaline Lipase of the Glyoxysomal Membrane Is a Glycoprotein
The presence of N-linked, high-mannose oligosaccharide on alkaline lipase has been demonstrated. Alkaline lipase in glyoxysomes of the endosperm of castor bean (Ricinus communiscv Hale) seedlings, is an intrinsic membrane protein, Mr62,000. The presence of glucosamine-containing oligosaccharides was shown directly by immunoprecipitat ion of lipase which had been labeledin vivoby14C-glucosamine. Lipase was eluted from concanavalin A-Sepharose at high concentration of α-methylglucoside indicating the presence of high mannose-type oligosaccharide. Two cross- reacting polypeptides (CRPs) in the glyoxysomal membrane were also identified. The two glyoxysomal CRPs, 67 kD and 86 kD, did not bind the lectin column under non-denaturing conditions. Nevertheless, the CRPs which were also abundant in carbonate-stripped endoplasmic reticulum were intensely labeled by14C-glucosamine. Treatment with endo-β-N-acetylglucosaminidase H confirmed the presence of N-linked, high mannose oligosaccharide. The possible relationship of the cross-reacting glycopolypeptides to the lipase is under study.
KeywordsCastor Bean Somal Membrane Intrinsic Membrane Protein Alkaline Lipase Lectin Affinity Chromatography
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