Coll M, Knof S H, Ohga Y, Messerschmidt A, Huber R, Moellering H, Rüssmann L, Schumacher G
Max-Planck-Institut fuer Biochemie, Martinsried bei Muenchen, F.R.G.
J Mol Biol. 1990 Jul 20;214(2):597-610. doi: 10.1016/0022-2836(90)90201-v.
Crystal structures of the enzyme creatine amidinohydrolase (creatinase, EC 3.5.3.3) with two different inhibitors, the reaction product sarcosine and the substrate creatine, bound have been analyzed by X-ray diffraction methods. With the inhibitor carbamoyl sarcosine, two different crystal forms at different pH values have been determined. An enzymatic mechanism is proposed on the basis of the eight structures analyzed. The enzyme binds substrate and inhibitor in a distorted geometry where the urea resonance is broken. His232 is the general base and acid, and acts as a proton shuttle. It withdraws a proton from water 377 and donates it to the N(3) atom of the guanidinium group. OH- 377 adds to the C(1) atom of the guanidinium group to form a urea hydrate. Proton withdrawal by His232 leads to products. The reaction product sarcosine binds to the active site in a reverse orientation. The free enzyme was found to have a bicarbonate bound to the active site.
通过X射线衍射方法分析了肌酸脒基水解酶（肌酸酶，EC 3.5.3.3）与两种不同抑制剂（反应产物肌氨酸和底物肌酸）结合时的晶体结构。对于抑制剂氨基甲酰肌氨酸，已确定了在不同pH值下的两种不同晶体形式。基于所分析的八种结构提出了一种酶促机制。该酶以扭曲的几何结构结合底物和抑制剂，其中尿素共振被打破。His232是通用碱和酸，并充当质子穿梭体。它从水377中夺取一个质子并将其捐赠给胍基的N(3)原子。OH- 377添加到胍基的C(1)原子上形成尿素水合物。His232夺取质子导致产物形成。反应产物肌氨酸以相反的方向结合到活性位点。发现游离酶的活性位点结合有一个碳酸氢盐。
