Tatnell P J, Russell N J, Gacesa P
Department of Biochemistry, University of Wales, Cardiff, UK.
J Gen Microbiol. 1993 Jan;139(1):119-27. doi: 10.1099/00221287-139-1-119.
GDP-mannose dehydrogenase (GMD) is a key regulatory enzyme and the committal step in alginate biosynthesis. In this study, a metabolic approach has been used to investigate GMD activity in non-mucoid and isogenically related mucoid strains of Pseudomonas aeruginosa. Intracellular concentrations of GDP-mannose and GDP-mannuronate have been quantified using HPLC separation methods, and their concentrations have been related to GMD activity and total alginate production. In all strains of P. aeruginosa tested, GDP-mannose accumulated particularly during the exponential phase of growth in batch culture; the GDP-mannose concentrations in mucoid strains were significantly lower compared with isogenic non-mucoid strains. The product of GMD activity, GDP-mannuronate, was detectable only in mucoid strains, albeit at low but relatively constant levels irrespective of growth phase. The GDP-mannose concentrations in mucoid strains were always significantly greater than those of GDP-mannuronate, indicating that GMD is a rate-limiting enzyme in the biosynthesis of alginate. Significant GMD activity and extracellular alginate production were detected only in mucoid strains. The metabolic data reported here, together with previous genetic studies, provide strong evidence that GMD is the key regulatory enzyme controlling alginate biosynthesis in mucoid strains of P. aeruginosa.
GDP-甘露糖脱氢酶（GMD）是藻酸盐生物合成中的关键调节酶和关键步骤。在本研究中，采用代谢方法研究了铜绿假单胞菌非黏液型和同基因相关黏液型菌株中的GMD活性。利用高效液相色谱分离方法对GDP-甘露糖和GDP-甘露糖醛酸的细胞内浓度进行了定量，并且它们的浓度与GMD活性和藻酸盐总产量相关。在所有测试的铜绿假单胞菌菌株中，GDP-甘露糖尤其在分批培养的指数生长期积累；黏液型菌株中的GDP-甘露糖浓度与同基因非黏液型菌株相比显著较低。GMD活性产物GDP-甘露糖醛酸仅在黏液型菌株中可检测到，尽管其水平较低但在不同生长阶段相对恒定。黏液型菌株中的GDP-甘露糖浓度总是显著高于GDP-甘露糖醛酸的浓度，表明GMD是藻酸盐生物合成中的限速酶。仅在黏液型菌株中检测到显著的GMD活性和细胞外藻酸盐产生。此处报道的代谢数据与先前的遗传学研究一起，提供了强有力的证据表明GMD是控制铜绿假单胞菌黏液型菌株中藻酸盐生物合成的关键调节酶。
