• Citer

Co-operative interactions between the catalytic sites in Escherichia coli aspartate transcarbamylase. Role of the C-terminal region of the regulatory chains

par Xu, Guang Xi;Ladjimi, Moncef M.M.;Hervé, Guy;Van Vliet, Françoise ;De Wannemaeker, Bénédicte;De Staercke, Christine;Glansdorff, Nicolas ;Cunin, Raymond ;Pierard, André
Référence Journal of Molecular Biology, 216, 2, page (375-384)
Publication Publié, 1990-11

Article révisé par les pairs

• Accès en ligne
• Détails
• Contenu
• Statistiques

Résumé :

In aspartate transcarbamylase (ATCase) each regulatory chain interacts with two catalytic chains each one belonging to a different trimeric catalytic subunit (R1-C1 and R1-C4 types of interactions as defined in Fig. 1). In order to investigate the interchain contacts that are involved in the co-operative interactions between the catalytic sites, a series of modified forms of the enzyme was prepared by site-directed mutagenesis. The amino acid replacements were devised on the basis of the previously described properties of an altered form of ATCase (pAR5-ATCase) which lacks the homotropic co-operative interactions between the catalytic sites. The results obtained (enzyme kinetics, bisubstrate analog influence and pH studies) show that the R1-C4 interaction is essential for the establishment of the enzyme conformation that has a low affinity for aspartate (T state), and consequently for the existence of co-operativity between the catalytic sites. This interaction involves the 236-250 region of the aspartate binding domain of the catalytic chain (240s loop) and the 143-149 region of the regulatory chain which comprises helix H3′. © 1990 Academic Press Limited.