Eshete F, LoVerde P T
Department of Microbiology, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214.
J Parasitol. 1993 Jun;79(3):309-17.
It is proposed that the phenol oxidase enzyme of schistosomes and other trematodes has a crucial role in the cross-linking of precursor proteins in the formation of the eggshell. However, to date there is no direct evidence to show that the enzyme catalyzes the reactions necessary for the posttranslational modification of eggshell precursor proteins. In this report we demonstrate that an eggshell precursor protein acts as a substrate for a schistosome fraction that catalyzed the 2 steps in the oxidation of tyrosine. This action of the phenol oxidase-containing worm fraction resulted in the tyrosine-dependent insolubilization and aggregation of the protein, suggesting a role for the enzyme in the posttranslational modification and cross-linking of schistosome eggshell proteins. The enzyme-rich fraction from Schistosoma mansoni catalyzed both steps of the reactions necessary for the conversion of tyrosine residues on putative eggshell precursor protein (p48) to quinones. The parasite fraction also catalyzed the hydroxylation of free L-tyrosine to DOPA (monophenol oxidase activity) and the oxidation of L-DOPA to dopaquinone (diphenol oxidase activity). Both activities of the enzyme are avidly bound to membranous structures, are susceptible to agents known to inhibit a functionally related enzyme, tyrosinase, and may reside on the same protein.
有人提出，血吸虫和其他吸虫的酚氧化酶在卵壳形成过程中前体蛋白的交联中起关键作用。然而，迄今为止，尚无直接证据表明该酶催化卵壳前体蛋白翻译后修饰所需的反应。在本报告中，我们证明了一种卵壳前体蛋白可作为血吸虫组分的底物，该组分催化酪氨酸氧化的两个步骤。含酚氧化酶的虫体组分的这种作用导致蛋白质酪氨酸依赖性不溶性和聚集，表明该酶在血吸虫卵壳蛋白的翻译后修饰和交联中起作用。来自曼氏血吸虫的富含酶的组分催化了将假定的卵壳前体蛋白（p48）上的酪氨酸残基转化为醌所需反应的两个步骤。寄生虫组分还催化游离L-酪氨酸羟基化为多巴（单酚氧化酶活性）以及L-多巴氧化为多巴醌（二酚氧化酶活性）。该酶的两种活性都与膜结构紧密结合，易受已知抑制功能相关酶酪氨酸酶的试剂影响，并且可能存在于同一蛋白质上。
