Dainese E, Di Muro P, Beltramini M, Salvato B, Decker H
Department of Biology, University of Padova, Italy.
Eur J Biochem. 1998 Sep 1;256(2):350-8. doi: 10.1046/j.1432-1327.1998.2560350.x.
Carcinus aestuarii hemocyanin (Hc) exists in two aggregation forms at pH 7.5 and 20 mM Ca2+: 24S accounting for 90% of total hemocyanin and 16S accounting for 10%. Removal of metal cations by EDTA at neutral pH causes the complete dissociation of 24S hemocyanin into two different 16S. At pH 9.2, 24S hemocyanin dissociates into a pH stable 16S and a 5S component. The 5S component consists of three monomeric fractions named CaeSS1 (10%), CaeSS2 (50%) and CaeSS3 (40%); the latter fraction consisting of two isoforms. The fractions CaeSS1, CaeSS2 and CaeSS3 have been studied as far as their reassociation properties to form hexamers are concerned. We investigated the oxygen-binding properties of the native form (24S), the mixture of the two 16S forms, the pH-stable 16S alone and of purified subunit fractions to define the role of each species on the expression of the allosteric behaviour of the 24S aggregate. The analysis of O2-binding data reveals that 24S-Hc can be well described by the modified Monod Wyman and Changeaux-model (nested MWC-model), while the half-molecules (16S) bind oxygen according to the simple MWC-model. The two hexameric 16S within the dodecameric 24S hemocyanin can be regarded as nested allosteric units. They behave as being functionally coupled in the T-states (tT and rT). In the R-states (tR and rR) the two half-molecules seem to be functionally uncoupled since they have the same values of oxygen binding constants as deduced for isolated 16S hexamers.
河口滨蟹血蓝蛋白（Hc）在pH 7.5和20 mM Ca2+条件下以两种聚集形式存在：24S占血蓝蛋白总量的90%，16S占10%。在中性pH条件下用EDTA去除金属阳离子会导致24S血蓝蛋白完全解离为两种不同的16S。在pH 9.2时，24S血蓝蛋白解离为pH稳定的16S和5S组分。5S组分由三个单体级分组成，分别命名为CaeSS1（10%）、CaeSS2（50%）和CaeSS3（40%）；后一个级分由两种异构体组成。就形成六聚体的重新缔合特性而言，已对CaeSS1、CaeSS2和CaeSS3级分进行了研究。我们研究了天然形式（24S）、两种16S形式的混合物、单独的pH稳定16S以及纯化的亚基级分的氧结合特性，以确定每种物种在24S聚集体变构行为表达中的作用。对O2结合数据的分析表明，24S - Hc可以用改进的莫诺 - 怀曼 - 尚热模型（嵌套MWC模型）很好地描述，而半分子（16S）根据简单的MWC模型结合氧气。十二聚体24S血蓝蛋白中的两个六聚体16S可被视为嵌套的变构单元。它们在T态（tT和rT）中表现为功能耦合。在R态（tR和rR）中，两个半分子似乎功能解耦，因为它们的氧结合常数与分离的16S六聚体推导的值相同。
