SUBUNITS AND QUATERNARY STRUCTURE OF TRANSCARBOXYLASE

这项研究是亚基-亚基研究的继续 生物素酶，转羧酶的相互作用。这种酶是由 六聚体中心亚基的，看起来呈圆柱形。 六个二聚体外部亚基连接在这个 中央亚基，每面3个。外部与中心的联动 亚基由12个生物素亚基组成，每个外部二聚体亚基2个。这个 催化的反应是CH3CH(COO-)COSCoA+CH3COCOO-CH3CH2COSCoA+OOCCH2COCOO. CoA酯中心在中心亚基上，酮酸中心在 外亚基和生物素之间作为羧基载体 这些网站。在中央亚单位上，有12个位点通过 外部亚基通过生物素亚基的一部分连接，也是12 与生物素亚基的另一部分结合用于定向的部位 用于羧基转移的生物素，以及另外12个辅酶A酯 网站。因此，中央亚基的6个多肽中的每一个都具有双重 网站的3个不同的功能。这样做的目的是为了确定 生物素亚基的部分参与其各种功能。 这将通过化学合成选定的部分来实现 生物素亚基的序列测定及其个体调查 结合性能和催化性能。序列的互补序列 亚基-亚基所涉及的外亚单位和中心亚基 相互作用将通过将它们与生物素交联来研究。 亚单位。该酶的结构将通过X射线进行研究 结晶学和电子显微镜观察该酶晶体和 它的亚单位。长期目标是了解复杂程度有多高 一般情况下，酶是组装的，亚基是如何在 催化作用。生物素酶在碳水化合物和脂肪中起着核心作用。 新陈代谢和一些严重的临床症状出现时 酶缺乏。这项研究有助于理解 生物素酶的一般作用。

This investigation is a continuation of studies of the subunit-subunit interactions of the biotin enzyme, transcarboxylase. The enzyme is made up of a hexameric central subunit which appears to have cylindrical shape. Six dimeric outer subunits are attached at the opposite faces of this central subunit, 3 at each face. The linkage of the outer to the central subunit is via 12 biotinyl subunits, 2 per outer dimeric subunit. The reaction catalyzed is CH3CH(COO-)COSCoA+CH3COCOO-CH3CH2COSCoA+OOCCH2COCOO. The CoA ester sites are on the central subunit and the keto acid sites on the outer subunits and the biotin serves as a carboxyl carrier between these sites. On the central subunit, there are 12 sites through which the outer subunits are attached via a portion of the biotinyl subunit, also 12 sites for binding of another part of the biotinyl subunit for orientation of the biotin for the carboxyl transfer, and in addition 12 CoA ester sites. Thus, each of the 6 polypeptides of the central subunit has dual sites for the 3 separate functions. The aims are to determine which portions of the biotinyl subunit are involved in its various functions. This will be accomplished by chemical synthesis of selected parts of the sequence of the biotinyl subunit and investigation of their individual binding and catalytic properties. The complementary sequences of the outside and central subunit which are involved in the subunit-subunit interaction will be investigated by cross-linking them with the biotinyl subunit. The structure of the enzyme will be investigated by X-ray crystallography and by electron microscopy of crystals of the enzyme and its subunits. The long term goal is to gain understanding of how complex enzymes in general are assembled and how the subunits interact in catalysis. Biotin enzymes have a central role in carbohydrate and lipid metabolism and a number of serious clinical syndromes arise when these enzymes are deficient. The present study contributes to understanding of the role of biotin enzymes in general.