Aspán A, Huang T S, Cerenius L, Söderhäll K
Department of Physiological Botany, University of Uppsala, Sweden.
Proc Natl Acad Sci U S A. 1995 Feb 14;92(4):939-43. doi: 10.1073/pnas.92.4.939.
Prophenoloxidase (proPO), an enzyme that is the terminal component of the so-called proPO activating system, a defense and recognition system in crustaceans and insects, has been purified and cloned from a crayfish blood cell cDNA library. The deduced amino acid sequence codes for a polypeptide with a mass of 80,732 Da, which is close to 76 kDa, the apparent mass of the purified enzyme. proPO contains two copper atoms, and two putative copper-binding sites were found in the deduced amino acid sequence. Sequence comparisons show that these putative copper-binding sites are similar to the corresponding sites in arthropod hemocyanins and also, although the sequence similarities are less extensive, similar to tyrosinases from vertebrates and microorganisms. The purified enzyme is a typical tyrosinase because it hydroxylates monophenols and oxidizes o-diphenols but does not oxidize p-diphenols. If a homogeneous preparation of crayfish proPO were incubated with a homogeneous sample of the proPO activating enzyme, a serine proteinase, the cleavage of proPO by this trypsin-like enzyme was found to occur between Arg-176 and Thr-177.
酚氧化酶原（proPO）是一种酶，它是所谓的proPO激活系统的终端成分，该系统是甲壳类动物和昆虫的防御与识别系统，已从小龙虾血细胞cDNA文库中纯化并克隆出来。推导的氨基酸序列编码一个质量为80,732 Da的多肽，这与纯化酶的表观质量76 kDa接近。proPO含有两个铜原子，并且在推导的氨基酸序列中发现了两个假定的铜结合位点。序列比较表明，这些假定的铜结合位点与节肢动物血蓝蛋白中的相应位点相似，并且尽管序列相似性不太广泛，但也与脊椎动物和微生物的酪氨酸酶相似。纯化的酶是一种典型的酪氨酸酶，因为它能使单酚羟基化并氧化邻二酚，但不能氧化对二酚。如果将小龙虾proPO的纯化物与proPO激活酶（一种丝氨酸蛋白酶）的纯化物一起孵育，会发现这种类胰蛋白酶样酶对proPO的切割发生在精氨酸-176和苏氨酸-177之间。
