Catalytic properties and specificity of a recombinant, overexpressed d-mannuronate lyase

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• 作者：Chavagnat ; Fré ; dé ; ric ; Heyraud ; Alain ; Colin-Morel ; Philippe ; Guinand ; Micheline ; et. al.
• 关键词：Bacterial alginate lyase ; Mannuronate lyase ; AlxM_B
• 刊名：Carbohydrate Research
• 出版年：1998
• 出版时间：April, 1998
• 年：1998
• 卷：308
• 期：3-4
• 页码：409-415
• 全文大小：204 K

文摘

Lysis of alginates and of their saturated and unsaturated fragments was monitored by ¹H NMR spectroscopy. AlxM_B alginate lyase performs β-elimination on the mannuronic acid (M) residues. It does not cleave the guluronic acid (G) sequences, nor the M–G or the G–M diads. In consequence, it is a true mannuronate lyase. The end product of the reaction is O-(4-deoxy-α-l-erythro-hex-4-enopyranosyl-uronic acid)-(1→(4)-O-(β-d-mannopyranosyluronic acid)-(1→4)-O-β-d-mannopyranuronic acid. Viscosity measurements made during degradation of a polymannuronate alginate showed that AlxM_B behaves as an endo-enzyme. HPLC analysis of the degradation products of oligomannuronates and oligoalginates suggested that the β-elimination requires the interaction of the enzyme with at least three sequential mannuronic acid residues. The catalytic site may possess 5 sub-sites and accommodate pentamers with different M/G ratio. Kinetic measurements showed that the specificity constant V_m/K_m increased with the number of mannuronic acid residues. AlxM_B may be reversibly inhibited by heteropolymeric blocks in a competitive manner.