Insect extramitochondrial glycerophosphate dehydrogenase II. Enzymic properties and amino acid composition of the enzyme from honeybee (Apis mellifera) thoraces

Ronald W. Brosemer, Ronald R. Marquardt
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引用次数: 37

Abstract

Several enzymic properties of crystalline honeybee (Apis mellifera) thoracic glycerophosphate dehydrogenase (L-glycerol-3-phosphate:DPN+ oxidoreductase, EC 1.1.1.8) were determined. The apparent Michaelis constant for dihydroxyacetone phosphate is 0.33 mM; there is no increase in activity with substrate concn. above 0.5 mM.

The bee enzyme has a broad pH optimum around pH 6.6, while the rabbits-muscle enzyme has a sharp optimum at pH 7.7. The bee enzyme is stable for 15 min at 21° from pH 4.8 to 9.9.

The temperature coefficient, Q10, for the bee enzyme is 1.7 in the range from 21° 36°. The enzyme is stable for 5 min at 55° and completely inactivated at 61°. The bee enzyme shows the same relative reactivity with 2 DPN+ analogues as does the rabbit enzyme. The bee enzyme is inhibited by a low concentration of p-mercuribenzoate (PCMB), is less sensitive to N-ethylmaleimide, and is not inhibited by 1 mM iodoacetate. Glutathione does not activate the enzyme.

The amino acid composition of the bee enzyme is quite different from the previously reported composition of the rabbits-muscle enzyme. The minimum molecular weight of the bee enzyme based on 1 tryptophan residue is 32 700. Since the molecular weight determined on a Sephadex G-200 column is around 67 000, the amino acid composition indicates a mol. wt. of 65 400.

昆虫线粒体外甘油磷酸脱氢酶II。蜜蜂胸脯酶的性质和氨基酸组成
测定了结晶蜜蜂胸廓甘油磷酸脱氢酶(l-甘油-3-磷酸:DPN+氧化还原酶,EC 1.1.1.8)的几种酶学性质。磷酸二羟丙酮的表观米歇里斯常数为0.33 mM;与底物有关时,活性没有增加。蜜蜂酶在pH 6.6左右有广泛的最适pH值,而兔肌酶在pH 7.7左右有明显的最适pH值。蜜蜂酶在21°温度下从pH 4.8到9.9稳定15分钟。蜜蜂酶的温度系数Q10在21°36°范围内为1.7。酶在55°时稳定5min,在61°时完全失活。蜜蜂酶对2个DPN+类似物的相对反应性与兔酶相同。低浓度的对汞苯甲酸酯(PCMB)对蜜蜂酶有抑制作用,对n -乙基马来酰亚胺不太敏感,1 mM碘乙酸不受抑制。谷胱甘肽不能激活这种酶。蜜蜂酶的氨基酸组成与先前报道的兔肌酶的组成有很大不同。以1个色氨酸残基为基础的蜜蜂酶的最小分子量为32 700。由于在Sephadex G-200色谱柱上测定的分子量约为67 000,氨基酸组成表明摩尔重量为65 400。
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