β-Glucosidase 2 (GBA2) is a resident enzyme of the endoplasmic reticulum thought to play a role in the metabolism of bile acid-glucose conjugates. To gain insight into the biological function of this enzyme and its substrates, we generated mice deficient in GBA2 and found that these animals had normal bile acid metabolism. Knockout males exhibited impaired fertility. Microscopic examination of sperm revealed large round heads (globozoospermia), abnormal acrosomes, and defective mobility. Glycolipids, identified as glucosylceramides by mass spectrometry, accumulated in the testes, brains, and livers of the knockout mice but did not cause obvious neurological symptoms, organomegaly, or a reduction in lifespan. Recombinant GBA2 hydrolyzed glucosylceramide to glucose and ceramide; the same reaction catalyzed by the β-glucosidase acid 1 (GBA1) defective in subjects with the Gaucher's form of lysosomal storage disease. We conclude that GBA2 is a glucosylceramidase whose loss causes accumulation of glycolipids and an endoplasmic reticulum storage disease.

IntroductionThe aim of this study was to define whether N-acetylglucosaminidation is a selective conjugation pathway of structurally related bile acids in humans. The following bile acids released enzymatically from N-acetylglucosaminides were identified:3a,7,8-dihydroxy-5,j-cholanoic (ursodeoxycholic), 3#,7,6-dihydroxy-5ft-cholanoic (isoursodeoxycholic) (6,7,9,10 MethodsMaterials. The sources and the purity of most materials are described elsewhere (10, 1 1). Alloursodeoxycholic acid and methyl-3,7-diketo5a-cholanoate were kind gifts ofDrs. H. lida

A human liver microsomal ␤-glucosidase has been purified to apparent homogeneity in sodium dodecyl sulfate-polyacrylamide gel electrophoresis where a single protein band of M r 100,000 was obtained under reducing conditions. The enzyme was enriched about 73,000-fold over starting microsomal membranes by polyethylene glycol fractionation, anion exchange chromatographies on DEAE-Trisacryl, and Mono Q followed by affinity chromatography on N-(9-carboxynonyl)-1-deoxynojirimycin-AH-Sepharose 4B. The purified enzyme had a pH optimum between 5.0 and 6. Bile acid glucosides have been shown to be formed in human liver microsomes by a glucosyltransferase that is sugar nucleotide-independent and utilizes dolichyl phosphoglucose as natural cosubstrate (Ref.

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Abstract. Microsomal UDP-glucuronosyltransferase activity toward the bile acids (chenodeoxycholic, deoxycholic, ursodeoxycholic, lithocholic, and glycolithocholic) has been detected in human specimens of liver, kidney, and intestinal mucosa. The characteristics of hepatic and extrahepatic UDP-glucuronosyltransferase activities toward these bile acids were compared with respect to kinetic parameters and other catalytic properties. Whereas no organspecific differences in the affinities of individual bile acids to hepatic and extrahepatic UDP-glucuronosyltransferases were observed, the individual bile acids showed reaction rates in liver that were about twice the rates estimated in kidney and about twice to three times the rates observed in duodenal mucosa. In intestinal mucosa the rate of chenodeoxycholic acid glucuronidation exhibited a progressive decrease from duodenum to colon, where it was 30%o of the duodenal level.