BIOCHEMISTRY OF INVERTEBRATE HEMOGLOBINS

血红蛋白在大多数无脊椎动物中广泛但零星分布， 门这些血红蛋白中的大多数具有15-17 kDa的链，并且是 细胞内（分子< 65 kDa）或细胞外，质量达8000 kDa。一些节肢动物和软体动物的血红蛋白链由 2至20个通过肽键连接的肌红蛋白样结构域。许多 血红蛋白表现出高度合作的O2结合， 其他的是不合作的，完全独立于pH。 具有独特的功能，例如脊椎动物不具有的硫化物结合 血红蛋白组装和亚基间相互作用的模式是 完全不同于脊椎动物的血红蛋白。的非凡 形式和功能的多样性提供了一个有吸引力的系统， 研究基因结构、功能和进化以及蛋白质 结构和功能。我们的目标是了解 结构和功能，以及 确定某些簇的组织和核苷酸序列， 已被鉴定的珠蛋白基因。这些系统包括巨型， 200-亚单位细胞外血红蛋白的蚯蚓， 软体动物Barbatia和 Cardita和子囊菌的有趣的黄血红蛋白， 产氢菌，产碱菌。我们试图确定7个组成部分 蚯蚓血红蛋白的链组装形成高度合作的200 亚基分子，以及合作O2-结合是如何通过 变构调节剂、钙和质子。我们将学习，似乎大多数 不太可能，Cardita珠蛋白的18个结构域是否由独特的 RNA加工事件。如果域球蛋白的基因显示出预期的 重复的结构，那么差异应该表明一种模式， 重复。现有数据表明，这18个领域不仅非常 相似，但它们之间没有明显的氨基酸间隔区。的 基因结构应该允许评估不平等的可能作用， 交换和基因转换。植物的豆血红蛋白基因 3个内含子和4个外显子，与脊椎动物球蛋白基因相反， 只有两个内含子。现在唯一确定的无脊椎动物珠蛋白基因是 那些缺乏内含子的昆虫幼虫摇蚊和珠蛋白基因 来自蚯蚓，其内含子/外显子组织是 与脊椎动物的珠蛋白基因相同。的 真菌和细菌的黄素血红蛋白可能提供了一种进化上的联系 细胞色素和血红蛋白之间的联系我们希望，通过确定结构， 低等无脊椎动物的珠蛋白基因，以确定 外显子/内含子组织的变异并开发更好的 了解球蛋白的进化。

Hemoglobins are widely but sporadically distributed in most invertebrate phyla. Most of these hemoglobins have 15-17 kDa chains and are either intracellular (molecules < 65 kDa) or extracellular with masses to 8000 kDa. Some arthropods and molluscs have hemoglobins with chains composed of 2 to 20 myoglobin-like domains joined by peptide bonds. Many of the hemoglobins exhibit highly cooperative O2 binding and are strongly affected by pH. Others are non-cooperative and completely independent of pH. Some have unique functions such as sulfide binding not shared by vertebrate hemoglobins. The modes of assembly and inter-subunit interaction are totally different from those of vertebrate hemoglobins. The extraordinary diversity of both form and function provides an attractive system in which to investigate gene structure, function and evolution as well as protein structure and function. The goal is to understand the relationship between structure and function in selected invertebrate hemoglobins, and to determine the organization and nucleotide sequences of certain clusters of globin genes that have been identified. These systems include the giant, 200-subunit extracellular hemoglobins of the earthworm, Lumbricus, the multi-subunit, multidomain hemoglobins of the molluscs, Barbatia and Cardita and the intriguing flavohemoglobins of ascomycetous fungi and the hydrogen bacterium, Alcaligenes. We seek to determine how the 7 constituent chains of Lumbricus hemoglobin assemble to form a highly cooperative 200 subunit molecule, and how the cooperative O2-binding is modulated by the allosteric modulators, calcium and protons. We will learn, as seems most unlikely, whether the 18 domains of Cardita globin arose by unique RNA-processing events. If the genes of the domain globins show the expected repeating structures, then the differences should indicate a pattern of duplication. Existing data indicate not only that the 18 domains are very similar, but that no significant amino acid spacers occur between them. The gene structure should allow assessment of the possible roles of unequal crossing-over and gene conversion. The leghemoglobin genes of plants have 3 introns and 4 exons in contrast to the genes for vertebrate globins which have only 2 introns. The only invertebrate globin genes now determined are those of the insect larva Chironomus which lacks introns, and a globin gene from the earthworm Lumbricus, the intron/exon organization of which is identical with that of the globin genes of vertebrates. The flavohemoglobins of fungi and bacteria may provide an evolutionary link between cytochromes and hemoglobins. We hope, by determing the structures of selected globin genes of lower invertebrates, to determine the extent of variation of the exon/intron organization and to develop a better understanding of globin evolution.