Bicknell R, Waley S G
Biochem J. 1985 Oct 1;231(1):83-8. doi: 10.1042/bj2310083.
The kinetics of the hydrolysis of two cephalosporins by beta-lactamase I from Bacillus cereus 569/H/9 has been studied by single-turnover and steady-state methods. Single-turnover kinetics could be measured over the time scale of minutes when cephalosporin C was the substrate. The other substrate, 7-(2',4'-dinitrophenylamino)deacetoxycephalosporanic acid, was hydrolysed even more slowly, and has potential for use in crystallographic studies of beta-lactamases. Comparison of single-turnover and steady-state kinetics showed that, for both substrates, opening the beta-lactam ring (i.e. acylation of the enzyme) was the rate-determining step. Thus the non-covalent enzyme-substrate complex is expected to be the intermediate observed crystallographically.
利用单周转和稳态方法研究了蜡样芽孢杆菌569/H/9的β-内酰胺酶I对两种头孢菌素的水解动力学。以头孢菌素C为底物时,可在数分钟的时间尺度上测量单周转动力学。另一种底物7-(2',4'-二硝基苯氨基)去乙酰氧基头孢烷酸水解得更慢,有用于β-内酰胺酶晶体学研究的潜力。单周转和稳态动力学的比较表明,对于两种底物,β-内酰胺环的打开(即酶的酰化)是速率决定步骤。因此,非共价酶-底物复合物有望成为晶体学观察到的中间体。