Enzymatic Synthesis of Glucocerebroside by a Glucosyltransferase from Embryonic Chicken Brain

A glucosyltransferase that catalyzes the synthesis of glucosylceramide (glucocerebroside) from ceramide (N-acylsphingosine) and UDP-glucose was isolated from 13- to 14-day-old embryonic chicken brain. The reaction is the following: Ceramide + UDP-glucose → glucosylceramide (+ UDP) Ceramide was the most effective lipid acceptor, and a variety of potential donors could not replace UDP-glucose. The Km values for ceramide and UDP-[14C]glucose were 0.08 mm and 0.12 mm, respectively. Metal ions did not stimulate the reaction, and it was not inhibited by ethylenediaminetetraacetate. The particulate preparation of UDP-glucose:ceramide glucosyltransferase showed an absolute requirement for detergent, and optimal activity was obtained with a mixture of Cutscum and Triton X-100. The glucosyltransferase was detectable in brains from chick embryos as early as 7 days old; maximal activity was detected between 13 and 17 days of embryonic development. The enzyme catalyzes the first step in the synthesis of gangliosides.