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W Van Dijk

Publications and source records attributed to W Van Dijk.

25 records · Page 2Linked to original sources
PubMed1984

On the presence of two non-specific nucleotide-sugar-hydrolysing enzymes in rat liver.

Evidence is presented for the occurrence of two different non-specific nucleotide-sugar hydrolases in rat liver and other rat tissues. These two enzymes (I and II) were separated by chromatography on a 5'-AMP-aminohexyl-Sepharose column. Enzyme I is most probably identical with phosphodiesterase I (EC 3.1.4.1). Enzyme II appeared to be identical with an enzyme described in literature as 'CMP-sialic acid hydrolase' [Kean & Bighouse (1974) J. Biol. Chem. 249, 7813-7823], since almost all activity with CMP-N-acetylneuraminate as substrate was recovered in this enzyme fraction. CMP-N-acetylneuraminate was a poor substrate for Enzyme I, whereas deoxythymidine-5'-p-nitrophenyl phosphate and all nucleoside-diphosphosugars tested were good substrates for both Enzyme I and II. Therefore it is suggested that CMP-N-acetylneuraminate is used as an additional substrate to discriminate between the activities of Enzyme I and II in homogenates or membrane preparations. The various substrates appeared to be competitive inhibitors of each other, suggesting that, in each enzyme preparation, only one enzyme is responsible for the hydrolysis of the various substrates. The dissimilar properties of the two enzymes are substantiated by studying the subunit molecular masses (Enzyme I, 125 kDa; Enzyme II, 50-55 kDa), the sensitivity towards Triton X-100, Sarkosyl and sodium dodecyl sulphate and towards trypsin treatment. It is discussed whether the alpha-N-acetylglucosamine phosphodiesterase described by Varki & Kornfeld [(1981) J. Biol. Chem. 256, 9937-9943] is identical with one of the nucleotide-sugar hydrolases described here.

Animals↗
PubMed1983

Increased glycosylation capacity in regenerating rat liver is paralleled by decreased activities of CMP-N-acetylneuraminate hydrolase and UDP-galactose pyrophosphatase.

In regenerating rat liver the activities of CMP-N-acetylneuraminate hydrolase and UDP-galactose pyrophosphatase were decreased to 40-50% of control values within 35 h after partial hepatectomy. In the same time period the activities of sialyltransferase and galactosyltransferase were increased, and the initial sharp decrease in the carbohydrate content of liver and serum glycoproteins was largely restored. The antiparallel nature of these events is suggestive of an involvement of nucleotide-sugar-hydrolysis enzymes in rat liver glycoprotein biosynthesis.

Animals↗
PubMed1983

Subcellular localization and tissue distribution of sialic acid precursor-forming enzymes.

The enzymes UDP-N-acetylglucosamine pyrophosphorylase, UDP-N-acetylglucosamine 2-epimerase, N-acetylmannosamine kinase, N-acetylglucosamine kinase and N-acetylglucosamine 2-epimerase, which are involved in the metabolism of N-acetylneuraminic acid, were studied in rat with regard to their subcellular localization and tissue distribution. The subcellular distribution studies in liver indicated that the enzymes are localized in the soluble cell fraction. In other tissues the comparison of enzyme activities in homogenates with that in high-speed supernatants led to a similar conclusion. UDP-N-acetylglucosamine pyrophosphorylase, N-acetylglucosamine kinase and N-acetylglucosamine 2-epimerase were detected in almost all tissues studied. UDP-N-acetylglucosamine 2-epimerase and N-acetylmannosamine kinase, two enzymes considered to be key enzymes in the N-acetylneuraminic acid biosynthesis, were detected only in sialoglycoprotein-secreting tissues, i.e. liver, salivary gland and intestinal mucosa. The low activity of the key enzymes in other tissues suggests that the biosynthetic pathway of N-acetylneuraminic acid is not the same in various tissues.

Animals↗
PubMed1977

CMP-N-acetylneuraminic acid hydrolase, an ectoenzyme distributed unevenly over the hepatocyte surface.

The regional localization of CMP-N-acetylneuramic acid hydrolase at the hepatocyte surface was studied by using plasma membranes and hepatocytes isolated from rat liver. 1. By homogenization of the rat liver plasma membrane preparations and subsequent discontinuous sucrose gradient centrifugation, one light and two heavy membrane fractions were obtained. The origin of these three subfractions is discussed based on the specific activities in the three fractions of 5'-nucleotidase, alakaline phosphatase and Mg2+-ATPase and on electron microscopic examination of the fractions. Evidence is given suggesting that the light fraction is derived from the bile canalicular surface of the plasma membrane, and that the heavy fractions are derived predominantly from the sinusoidal and lateral surfaces of the liver cell membrane. CMP-AcNeu hydrolase was present at highest specific activity in one of the heavy subfractions. Therefore it is concluded that CMP-AcNeu hdyrolase is located preferentially in the sinusoidal and/or lateral plasma membrane parts of the liver cell. 2. Experiments with intact and disintegrated hepatocytes isolated from rat liver indicated that CMP-AcNeu hydrolase is located at the surface of the cell membrane, with its functional group directed to the outside.

Animals↗