SUBUNITS AND QUATERNARY STRUCTURE OF TRANSCARBOXYLASE

本研究是亚基-亚基研究的继续 生物素酶，转羧酶的相互作用。 这种酶是由 一个六聚体的中心亚基，似乎有圆柱形。 六个二聚体外部亚基连接在这个 中央亚单位，每面3个。 外部与中心的联系 亚基由12个生物素亚基组成，每个外二聚体亚基2个。 的 催化的反应是CH 3CH（COO-）COSCoA+ CH 3COCOO-CH 3CH 2COSCoA + OOCCH 2COCOO。 CoA酯位点位于中心亚基上，酮酸位点位于 外部亚基和生物素作为羧基载体， 这些网站。 在中央亚基上，有12个位点， 外部亚基通过生物素基亚基的一部分连接，也是12 用于结合生物素基亚基的另一部分以进行定向的位点 用于羧基转移的生物素，以及另外的12 CoA酯 网站. 因此，中心亚基的6个多肽中的每一个具有双重结构。 用于3个独立功能的站点。 其目的是确定 部分生物素基亚基参与其各种功能。 这将通过化学合成本发明化合物的选定部分来实现。 生物素基亚基的序列及其个体的研究 结合和催化性能。 的互补序列。 参与亚基-亚基的外部和中央亚基 将通过将它们与生物素基交联来研究相互作用。 亚单位 酶的结构将通过X射线研究 晶体学和电子显微镜的酶的晶体， 其子单位。 长期目标是了解 酶一般是组装的，以及亚基如何在 催化作用 生物素酶在碳水化合物和脂质中具有核心作用 代谢和一些严重的临床综合征出现时，这些 酶缺乏。 本研究有助于了解 生物素酶的作用。

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.