Cooperative effects in the binding of pyridoxal 5′‐phosphate to mitochondrial apo‐aspartate aminotransferase

FEBS Letters

Garzillo, A.M.¹  Marino, G.¹  Pispisa, B.¹ 

[1] Istituto di Chimica Organica e Biologica and Istituto Chimico, Università di Napoli, Via Mezzocannone 16, 80134 Napoli, Italy

关键词: Aspartate aminotransferase;    Pyridoxal 5′-phosphate;    AMP;    Cooperativity;   

DOI  :  10.1016/0014-5793(84)81317-4

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

Titrations of mitochondrial apo-aspartate aminotransferase with pyridoxal 5′-phosphate in the presence of AMP, contrary to what has been observed in the case of the cytosolic isoenzyme [(1983) FEBS Lett. 153, 98–102], show sigmoidal isotherms, with Hill coefficients ranging from n _H = 1.4, in the absence of AMP, to n _H = 1.8, in the presence of 5.9 mM AMP. The experimental data were successfully fitted by the Monod-Wyman-Changeaux model. The best fit, in the absence of AMP, was obtained with L = 30, K _R = 4.72 × 10⁻⁷ M and K _T = 1.18 × 10⁻⁵ M. Binding curves in the presence of AMP fit the model by keeping K _R as a constant. This implies that AMP could bind to the apoenzyme only in the T state. In contrast, binding curves in the presence of phosphate ion (P_i) showed a less pronounced cooperativity, the Hill coefficient dropping to n _H = 1.0 in the presence of 0.1 mM P_i. The above results suggest a regulatory role of AMP and P_i in the reconstitution of aspartate aminotransferase.

【 授权许可】

Unknown