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Partial purification and kinetic properties of three different D-glucosamine 6-P:N-acetyltransferase forms from human placenta.

Authors
  • Vessal, M
  • Jaberi-Pour, M
Type
Published Article
Journal
Comparative Biochemistry and Physiology Part B Biochemistry and Molecular Biology
Publisher
Elsevier
Publication Date
Dec 01, 1998
Volume
121
Issue
4
Pages
379–384
Identifiers
PMID: 9972309
Source
Medline
License
Unknown

Abstract

Three distinct forms of D-glucosamine 6-D (Gm 6-P):N-acetyltransferases (EC 2.3.1.4) were partially purified from human placental homogenates by carboxy methyl-Sephadex chromatography. Purification of forms I and II were 13.5-fold, while that of form III was 114-fold. All three forms had a pH optimum value of 9.7 in glycine-NaOH buffer. Enzymes II and III had a K(m) value for Gm 6-P of 3.0 mM, which was less than half of that observed for form I (7.1 mM). The corresponding K(m) values for acetyl CoA were 0.157 (form I), 0.187 (form II) and 0.280 mM (form III), respectively. Activities of all three forms were inhibited at high concentrations of either substrate. These enzymes were inhibited from 82 to 92% by 2.5 mM p-chloromercuribenzoate. The inhibition was largely reversible by inclusion of 2.5 mM dithiothreitol in the incubation mixtures. There was no requirement for divalent cations, as demonstrated by lack of inhibition of enzyme activity by ethylene diamine tetraacetate. The results are discussed in terms of differences among the enzyme properties of human placental, rodent and porcine liver forms.

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