Enzymological Characterization of the Pasteurella multocida Hyaluronic Acid Synthase
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- 作者：Paul L. DeAngelis
- 刊名：Biochemistry
- 出版年：1996
- 出版时间：July 30, 1996
- 年：1996
- 卷：35
- 期：30
- 页码：9768 - 9771
- 全文大小：245K
- 年卷期：v.35,no.30(July 30, 1996)
- ISSN：1520-4995
文摘
Hyaluronic acid (HA), a linear polysaccharide composed ofalternating glucuronic acid andN-acetylglucosamine residues, is an essential molecule ofhigher vertebrates. The fowl cholera pathogenPasteurella multocida Carter Type A also produces HA in theform of an extracellular capsule in orderto evade host defenses. HA synthase activity could be obtainedfrom cell-free membrane preparations ofP. multocida. The enzyme utilized UDP-sugarprecursors of HA in the presence of Mg2+ orMn2+ atneutral pH. Mn2+ at 1 mM stimulated ~2-fold moreincorporation than Mg2+ at 10 mM. On theotherhand, the analogous enzyme from group A Streptococcus, HasA,is stimulated more by Mg2+ thanMn2+.The apparent Michaelis constants, KM, of theP. multocida HA synthase forUDP-N-acetylglucosamineand UDP-glucuronic acid were estimated to be ~75 and ~20 
M,respectively, in the presence of Mg2+,which suggests that the substrates are bound with 2-3-fold higheraffinity than by the HasA enzyme.The rate enhancement observed with Mn2+ isapparently not due to better binding of the sugarnucleotideprecursors complexed to Mn ion because the KMvalue, a measure of substrate affinity, increases by25-50% in comparison to Mg2+. In summary, the HAsynthase from P. multocida, aGram-negativebacterium, has kinetic optima distinct from those of HasA, the analogfrom the Gram-positive group AStreptococcus.
M,respectively, in the presence of Mg2+,which suggests that the substrates are bound with 2-3-fold higheraffinity than by the HasA enzyme.The rate enhancement observed with Mn2+ isapparently not due to better binding of the sugarnucleotideprecursors complexed to Mn ion because the KMvalue, a measure of substrate affinity, increases by25-50% in comparison to Mg2+. In summary, the HAsynthase from P. multocida, aGram-negativebacterium, has kinetic optima distinct from those of HasA, the analogfrom the Gram-positive group AStreptococcus.