Formation of bilirubin glucoside

1. Rat liver microsomal preparation can effect the transglucosylation from UDP-glucose to bilirubin in the presence of Mg(2+). 2. Other nucleotides, namely CDP-glucose, ADP-glucose and GDP-glucose, were not active as glucosyl donors. 3. Only trace amounts of galactose, galacturonic acid and N-acetylglucosamine were conjugated to bilirubin when their respective UDP derivatives were used in the reaction mixture. 4. The azobilirubin glucosides produced by coupling with p-diazobenzenesulphonic acid and diazotized ethyl anthranilic acid were separable from the corresponding azobilirubin glucuronides by t.l.c. 5. The glucoside was, however, hydrolysed by both beta-glucosidase and various preparations of beta-glucuronidase; azobilirubin and glucose were liberated in the process. 6. Kinetic studies showed that the effects of pH and Mg(2+) on the two conjugating systems were similar. 7. The specific activities of hepatic bilirubin UDP-glucosyltransferase, expressed as mug of bilirubin ;equivalents' conjugated/h per mg of protein, are respectively 1.7 and 2.4 for male and female rats. 8. The K(m) values for bilirubin and UDP-glucose are 5.7x10(-5)m and 1.6x10(-3)m respectively. 9. The glucoside and glucuronide conjugations of bilirubin are discussed in relation to the availability of the conjugating agents and aglycone in the liver.

Biological and physical properties of a human m-cryoglobulin and its monomer subunit

A patient with Waldenstrom's macroglobulinaemia was found to have a serum cryoprecipitate which consisted entirely of a γMK-macroglobulin. This protein had no detectable antibody activity against a variety of other serum components and fixed only minimal amounts of complement over temperatures ranging from 4°C to 37°C. Precipitation of the cryoglobulin began at about 30°C and was complete at temperatures below 20°C. In contrast to other macroglobulins that have been reported, cryoprecipitability persisted after the protein was dissociated into its monomer subunits. Isolated subunits formed cryoprecipitates as did the hybrid macroglobulin formed from equal parts of such subunits and the subunits of a non-cryoprecipitating macroglobulin.

Carbohydrate content of the cryoglobulin was 12·81%, a value similar to γM molecules in general. Enzymatic removal of a portion of the carbohydrate caused the protein to become insoluble at even higher temperatures.

A single type of intermolecular binding responsible for cryoprecipitation could not be defined. Addition of salt or non-polar solvent, or change in pH had little effect on cryoprecipitability at 4°C, but all of these measures did cause an increased solubility at 24°C, a transitional temperature for cryoprecipitability. Addition of a variety of serum proteins and glycine also served to increase protein solubility. These data suggest that cryoprecipitation may involve both hydrophobic and electrostatic bonds. Temperature induced changes in molecular configuration might also indirectly influence cryoprecipitation by altering the binding site.

Excretion in dog bile of glucose and xylose conjugates of bilirubin

1. T.l.c. with neutral solvent systems of ethyl anthranilate azopigments derived from bile of man, dog and rat revealed pronounced species variation. The less polar components (alpha-group) could be separated conveniently by development with chloroform-methanol (17:3, v/v). 2. The azopigment material derived from gallbladder bile of dog contained about 10% of azobilirubin beta-d-monoxyloside (azopigment alpha(2)) and 30% of azobilirubin beta-d-monoglucoside (azopigment alpha(3)). The sugar moieties were identified by t.l.c. with acidic, neutral and basic solvent systems and by anion-exchange column chromatography of their boric acid complexes. Treatment of the purified azopigments with ammonia vapour led to the formation of the amide of azobilirubin, indicating that both pigments are ester glycosides. The beta-d configuration was demonstrated by enzymic studies with emulsin (an adequate source of beta-glucosidase activity) and with Mylase-P (an adequate source of beta-glucosidase and beta-xylosidase activities). 3. Hydrolysis studies with model substrates and with the alpha(2)- and alpha(3)-azopigments suggested that in Mylase-P the beta-glucosidase and beta-xylosidase activities reside in separate enzymes. 4. Compared with the accepted conjugation with glucuronic acid as a major route of detoxication in mammals, the detection of large amounts of xylose and glucose conjugates of bilirubin in dog bile suggests that the underlying biosynthetic pathways may be important alternative routes of detoxication.

The oligosaccharide units of a human type L immunoglobulin M (Macroglobulin)

1. The carbohydrate composition of the monomeric unit of a type L macroglobulin (immunoglobulin M) was determined as 6 residues of fucose, 35 of mannose, 11 of galactose, 27 of N-acetylglucosamine and 9 of sialic acid. 2. Two types of oligosaccharide unit were present in the protein, one of which (Ca type) contained fucose, mannose, galactose, N-acetylglucosamine and sialic acid in the molar proportions 1:3-4:2:3-5:0-2, and the other (Cb type) contained mannose and N-acetylglucosamine in the proportions 6-8:2-3. 3. A tentative structure is proposed for the Cb type unit. 4. An S-carboxymethylcysteine-containing glycopeptide with a Ca-type unit was isolated after reduction, alkylation and tryptic digestion of the protein. 5. The immunoglobulin monomer appears to contain six oligosaccharide units of the Ca type and two of the Cb type.

Structure of glycoproteins of human erythrocytes. Alkali-stable oligosaccharides

Studies have been made on the oligosaccharide residues of the alkali-stable carbohydrate-protein linkage of sialoglycopeptides derived from human erythrocytes. Four glycopeptides were isolated after alkaline borohydride treatment and Pronase digestion of MN-active sialoglycopeptides. The structure of one of these glycopeptides (GPIV) has been studied by sequential hydrolysis with specific glycosidases. Glycopeptide GPIV contained (per mol): 1mol of fucose, 1mol of sialic acid, 3mol of galactose, 3mol of mannose, 4mol of acetylglucosamine, 1mol of aspartic acid and fractional amounts of threonine, serine and glycine. The molecular weight of the glycopeptide was estimated to be 2330 by gel filtration. On the basis of glycosidase-digestion results, a tentative structure is proposed for the oligosaccharide moiety of glycopeptide GPIV.

The structure of a glycopeptide purified from porcine thyroblobulin

1. The structure of a purified glycopeptide isolated from porcine thyroglobulin was studied by sequential hydrolysis with specific glycosidases, by periodate oxidation and by treatment with galactose oxidase. 2. Sequential hydrolysis with several combinations of neuraminidase, alpha-l-fucosidase, beta-d-galactosidase, beta-N-acetyl-d-glucosaminidase and alpha-d-mannosidase presented the evidence for the following structure. 3. The monosaccharide sequence of the peripheral moiety of the heteropolysaccharide chain was sialic acid-->galactose-->N-acetylglucosamine. Some of the galactose residues were non-reducing end-groups with the sequence galactose-->N-acetylglucosamine. 4. After removal of the peripheral moiety composed of sialic acid, fucose, galactose and N-acetylglucosamine, alpha-mannosidase released 1.4mol of mannose/mol of glycopeptide, indicating that two of the three mannose residues were located between peripheral N-acetylglucosamine and internal N-acetylglucosamine or mannose. 5. Periodate oxidation and sodium borohydride reduction confirmed the results obtained by enzymic degradation and gave information concerning the position of substitution. 6. Based on the results obtained by enzymic hydrolysis and periodate oxidation together with the treatment with galactose oxidase, a structure is proposed for the glycopeptide.