Zhang J H, Kurtz D M
Department of Chemistry, University of Georgia, Athens 30602.
Biochemistry. 1991 Sep 24;30(38):9121-5. doi: 10.1021/bi00102a001.
Reported are results on the subunit composition of octameric hemerythrin (Hr) from the brachiopod Lingula reevii. Unlike most other Hrs, L. reevii Hr shows cooperativity in O2 binding. Purified L. reevii Hr was found to consist of two different subunits in approximately equimolar proportions. These two subunits differ in molecular weight by approximately 1000. Amino acid sequence data for the first 24 residues of the two subunits, labeled alpha and beta, show 70% identity with each other. Comparisons to amino acid sequences of other Hrs show approximately 50% identity in the first 24 residues and that both the alpha and beta subunits of L. reevii Hr have one residue deleted at their amino termini. Very recently, one other Hr, that from the brachiopod Lingula unguis, was also shown to contain equimolar proportions of two different subunits [Satake, K., Yugi, M., Kamo, M., Kihara, H., & Tsugita, A. (1990) Protein Seq. Data Anal. 3, 1-5], and this Hr also shows cooperativity in O2 binding. An alpha 4 beta 4 octamer is, therefore, proposed to be a common feature of those Hrs that show such cooperativity. Likely arrangements of alpha and beta subunits within an alpha 4 beta 4 octamer having the same configuration of subunits as that in other octameric Hrs are proposed. The most probable arrangements can be readily derived from physically reasonable restrictions on the types of intersubunit interactions and on transmission of allosteric effects.
报道了来自腕足动物 Reeves 舌形贝的八聚体血蓝蛋白（Hr）的亚基组成结果。与大多数其他 Hr 不同，Reeves 舌形贝 Hr 在氧气结合方面表现出协同性。纯化后的 Reeves 舌形贝 Hr 被发现由两种不同的亚基组成，比例大致相等。这两种亚基的分子量相差约 1000。标记为α和β的两种亚基前 24 个残基的氨基酸序列数据显示，它们彼此间有 70%的同一性。与其他 Hr 的氨基酸序列比较表明，在前 24 个残基中约有 50%的同一性，并且 Reeves 舌形贝 Hr 的α和β亚基在其氨基末端都有一个残基缺失。最近，另一种 Hr，即来自 Unguis 舌形贝的 Hr，也被证明含有等摩尔比例的两种不同亚基[Satake, K., Yugi, M., Kamo, M., Kihara, H., & Tsugita, A. (1990) Protein Seq. Data Anal. 3, 1 - 5]，并且这种 Hr 在氧气结合方面也表现出协同性。因此，有人提出α4β4 八聚体是那些表现出这种协同性的 Hr 的共同特征。本文提出了α4β4 八聚体内α和β亚基的可能排列方式，其亚基构型与其他八聚体 Hr 相同。最可能的排列方式可以很容易地从对亚基间相互作用类型和变构效应传递的合理物理限制中推导出来。
