Alpha 1--greater than 2 fucosyltransferase of human bone marrow

Purification, properties and possible gene assignment of an alpha 1,3-fucosyltransferase expressed in human liver

alpha 1,3-Fucosyltransferase solubilized from human liver has been purified 40,000-fold to apparent homogeneity by a multistage process involving cation exchange chromatography on CM-Sephadex, hydrophobic interaction chromatography on Phenyl Sepharose, affinity chromatography on GDP-hexanolamine Sepharose and HPLC gel exclusion chromatography. The final step gave a major protein peak that co-chromatographed with alpha 1,3-fucosyltransferase activity and had a specific activity of approximately 5-6 mumol min-1 mg-1 and an M(r) approximately 44,000 deduced from SDS-PAGE and HPLC analysis. The purified enzyme readily utilized Gal beta 1-4GlcNAc, NeuAc alpha 2-3Gal beta 1-4GlcNAc and Fuc alpha 1-2Gal beta 1-4GlcNAc, with a preference for sialylated and fucosylated Type 2 acceptors. Fuc alpha 1-2Gal beta 1-4Glc and the Type 1 compound Gal beta 1-3GlcNAc were very poor acceptors and no incorporation was observed with NeuAc alpha 2-6Gal beta 1-4GlcNAc. A polyclonal antibody raised against the liver preparation reacted with the homologous enzyme and also with the blood group Lewis gene-associated alpha 1,3/1,4-fucosyltransferase purified from the human A431 epidermoid carcinoma cell line. No cross reactivity was found with alpha 1,3-fucosyltransferase(s) isolated from myeloid cells. Examination by Northern blot analysis of mRNA from normal liver and from the HepG2 cell line, together with a comparison of the specificity pattern of the purified enzyme with that reported for the enzyme expressed in mammalian cells transfected with the Fuc-TVI cDNA, suggests a provisional identification of Fuc-TVI as the major alpha 1,3-fucosyltransferase gene expressed in human liver.

Blood group antigens on human erythrocytes-distribution, structure and possible functions

Human erythrocyte blood group antigens can be broadly divided into carbohydrates and proteins. The carbohydrate-dependent antigens (e.g., ABH, Lewis, Ii, P1, P-related, T and Tn) are covalently attached to proteins and/or sphingolipids, which are also widely distributed in body fluids, normal tissues and tumors. Blood group gene-specific glycosyltransferase regulate the synthesis of these antigens. Protein-dependent blood group antigens (e.g., MNSs, Gerbich, Rh, Kell, Duffy and Cromer-related) are carried on proteins, glycoproteins and proteins with glycosylphosphatidylinositol anchor. The functions of these molecules on human erythrocytes remain unknown; some of them may be involved in maintaining the erythrocyte shape. This review describes the distribution, structures and probable biological functions of some of these antigens in normal and pathological conditions.

Reassessment of the acceptor specificity and general properties of the Lewis blood-group gene associated alpha-3/4-fucosyltransferase purified from human milk

The acceptor specificity and general properties of a Lewis blood-group gene associated alpha-3/4-L-fucosyltransferase isolated from human milk have been examined at the penultimate purification stage involving affinity chromatography on GDP-hexanolamine Sepharose, and after a subsequent gel filtration step on Sephacryl S-200. Both preparations transferred fucose to the O-4 position of N-acetylglucosamine in Type 1 (Gal beta 1-3GlcNAc-R) acceptors and the O-3 position of glucose in lactose-based (Gal beta 1-4Glc) oligosaccharides, and both used Type 1 sialylated compounds when the terminal N-acetylneuraminic acid was present in alpha-2,3 linkage. The striking difference between the two preparations was in their reactivity with Type 2 (Gal beta 1-4GlcNAc-R) chains; after Sephacryl S-200 chromatography the apparent KM values for the alpha-3/4- preparation with unsubstituted low-molecular-weight Type 2 oligosaccharides were considerably increased. Substitution of the terminal galactose with sialic acid in alpha-2,3 linkage decreased the KM values for low-molecular-weight oligosaccharides but no detectable incorporation of fucose was observed into N-acetyllactosamine end-groups of glycoproteins with N-linked oligosaccharide chains, irrespective of the presence of sialic acid in the terminal sequences.

Synthesis of 2-acetamido-2-deoxy-4-O-(2-O-methyl-beta-D-galactopyranosyl)- D-glucopyranose (N-acetyl-2'-O-methyllactosamine)

1,3,4,6-Tetra-O-acetyl-2-O-methyl-D-galactopyranose, prepared from known methyl 6-O-acetyl-3,4-O-isopropylidene-beta-D-galactopyranoside, was treated with hydrogen bromide in dichloromethane to afford 3,4,6-tri-O-acetl-2-O-methyl-alpha-D-galactopyranosyl bromide. Condensation with benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside in acetonitrile in the presence of mercuric cyanide gave an approximately 1:1 mixture of benzyl 2-acetamido-3, 6-di-O-benzyl-2-deoxy-4-O-(3,4,6-tri-O-acetyl-2-O-methyl-beta- (8) and -alpha-D-galactopyranosyl)-alpha-D-glucopyranoside. O-Deacetylation and catalytic hydrogenolysis of the benzyl group furnished 2-acetamido-2-deoxy-4-O-(2-O-methyl-beta- and alpha-D-galactopyranosyl)-D-glucopyranose. Alternatively, benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-beta-D- galactopyranosyl-alpha-D-glucopyranoside was treated with tert-butyldiphenyl-chlorosilane in N,N-dimethylformamide, in the presence of imidazole, to give a 6'-O-tert-butyldiphenylsilyl intermediate that was in turn converted into its 3',4'-O-isopropylidene acetal. Methylation with methyl iodide-silver oxide in N,N-dimethylformamide, followed by removal of the silyl and isopropylidene groups gave benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-(2-O-methyl-beta-D- galactopyranosyl)-alpha-D-glucopyranoside, which was further characterized as its triacetate 8.

Use of N-acetyl-2'-O-methyllactosamine as a specific acceptor for the determination of alpha-L-(1----3)-fucosyltransferase in human serum

A synthetic substrate, N-acetyl-2'-O-methyllactosamine, was employed as a specific acceptor for alpha-L-(1----3)-fucosyltransferase from human serum. The fucosyl linkage of the product from this substrate was characterized by hydrolysis with a specific alpha-L-(1----3)/(1----4)-fucosidase. Using this acceptor, the pH optimum for the serum alpha-L-(1----3)-fucosyltransferase was 6.5. The enzyme was activated by Mn2+ or Mg2+ ions and was inhibited by EDTA. The apparent Km for this enzyme using N-acetyl-2'-O-methyllactosamine was 20.4 mM and Vmax was 5.6 pmol/h/ml serum.

Immunochemical properties of human plasma alpha 1 leads to 2 fucosyltransferase specified by blood group H-gene

A beta-galactoside alpha 1 leads to 2 fucosyltransferase (H-enzyme) from human group O plasma which provides H blood group specificity to erythrocyte membranes has been purified approximately 22,000-fold by chromatography on DEAE-Sepharose CL-6B, GDP-hexanolamine-Sepharose 4B and SP-Sephadex C-50. The molecular weight of the H-enzyme was estimated to be 150,000 by gel filtration. Human group O erythrocyte membranes which had lost their H blood group activity by the action of alpha 1 leads to 2 fucosidase were fucosylated by the transferase, and restored the H activity. Radioactive L-fucose appeared to be incorporated into glycolipid blood group substances of erythrocyte membranes. The activity of the alpha 1 leads to 2 fucosyltransferase from human plasma, stomach mucosa, erythrocyte membranes and porcine stomach mucosa were specifically inhibited by the rabbit antiserum immunized with the preparation of human plasma H-enzyme. The anti-plasma H-enzyme antiserum did not inhibit the activities of alpha 1 leads to 3 N-acetylgalactosaminyltransferase (A-enzyme), alpha 1 leads to 3 galactosyltransferase (B-enzyme), and beta-N-acetylglucosaminide alpha 1 leads to 3 and alpha 1 leads to 4 fucosyltransferases from human plasma and stomach mucosa.

Detection and activity of blood group B gene-associated alpha-galactosyltransferase in human urine

alpha-Galactosyltransferase which participates in the biosynthesis of blood group B substance was found in urine from group B and AB healthy persons of both secretors and non-secretors. The activity of alpha-galactosyltransferase in the urine of a healthy variant Bm person was lower than that found in a normal group B person. This enzyme in urine of A1Bm persons must be much lower than that in normal AB persons. Its activity was not detected by the method of group O to group B transformation or erythrocytes.

alpha-L-Fucosyltransferases related to biosynthesis of blood group substances in human Saliva

alpha-L-Fucosyltransferases were demonstrated in human saliva which catalyze the transfer of L-fucose from GDP-L-[14C]-fucose to oligosaccharides from human milk. An alpha-(1 yields 4)-L-fucosyltransferase that synthesizes lacto-N-fucopentaose II and lacto-N-difucohexaose I from lacto-N-tetraose and lacto-N-fucopentaose I, respectively, was detected in saliva samples of Le(a--b+) secretors and Le(a+b--) non-secretors in which Lea substance was secreted. This enzyme activity was demonstrable neither in saliva samples of Le(a--b--) secretors nor non-secretors. An alpha-(1 yields 2)-L-fucosyltransferase, that synthesizes lacto-N-fucopentaose I from lacto-N-tetraose, was detected in saliva samples from Le(a--b+) secretors which secreted H and Leb substances and from Le(a--b--) secretors which secreted only H substance. An alpha-(1 yields 3)-L-fucosyltransferase was present in all saliva samples of different ABO and Lewis blood groups, irrespective of their ABH secretor status of the donors. The fucosyltransferases in saliva were activated by Mn++ or Mg++ ions, and were inhibited by ATP, GTP and EDTA. They had a broad pH optimum between pH 5.0 and 6.5.

Delineation of fucosyltransferase activities with thiol reagents

The thiol reagent dithiothreitol inhibits the activity of a core GDP-fucose-N-acetylglucosaminide alpha-6-fucosyltransferase in plasma and blood-cell homogenates, while promoting the activity of alpha-2- and alpha-3-fucosyltransferases. The latter enzymes catalyse transfer of fucose on to terminal galactose and subterminal N-acetylglucosamine residues respectively. A thiol-blocking reagent N-ethylmaleimide does not affect the activity of the alpha-6-fucosyltransferase, but inhibits the other two enzymes. These results indicate the presence of a critical disulphide linkage in the alpha-6-fucosyltransferase, and provide a means of delineation of different fucosyltransferases.

Enzymatic synthesis of two fucose-containing glycolipids with fucosyltransferases of human serum

Lacto-N-neotetraosylceramide incubated with human serum fucosyltransferase preparations gave rise to two fucoglycolipids. The faster migrating fucoglycolipid I on the basis of its thin-layer chromatographic mobility, susceptibility to alpha(1 leads to 2) fucosidase from Trichomonas foetus, radio-immunoprecipitation with Ulex europeus lectin and studies with Oh (Bombay) sera was identified as H-active glycolipid (H-I). The most probable structure of fucoglycolipid II should be that with fucose linked alpha(1 leads to 3) to N-acetylglucosamine. Lactosylceramide, ceramide trihexoside and globoside were not substrates for human serum fucosyltransferases. Lacto-N-neotetraosyl ceramide served as a fucose acceptor for all serum preparations tested while asialoganglioside was a substrate only when serum preparations containing H-gene dependent alpha-2-L-fucosyltransferase were used. With asialoganglioside only one radioactive reaction product was formed.

Activity of B-gene-specified galactosyltransferase in individuals with Bm phenotypes

Blood group B-gene-specified alpha-galactosyltransferase was determined in serums and erythrocyte membranes of several related persons with Bm phenotypes. The level of this enzyme in serums was similar to, but in erythrocyte membranes much lower than that found in normal B and AB persons.