Hari Krishna S, Karanth N G
Fermentation Technology and Bioengineering Department, Central Food Technological Research Institute, 570 013, Mysore, India.
Biochim Biophys Acta. 2001 Jun 11;1547(2):262-7. doi: 10.1016/s0167-4838(01)00194-7.
Kinetics of lipase-catalyzed esterification of butyric acid and isoamyl alcohol have been investigated. The reaction rate could be described in terms of the Michaelis-Menten equation with a Ping-Pong Bi-Bi mechanism and competitive inhibition by both the substrates. No evidence of any significant diffusional limitations was detected that could affect the kinetics. The values of the apparent kinetic parameters were computed as: V(max)=11.72 micromol/min/mg; K(M, Acid)=0.00303 M; K(M, Alcohol)=0.00306 M; K(i, Acid)=1.05 M; and K(i, Alcohol)=6.55 M. This study indicates a competitive enzyme inhibition by butyric acid during lipase-catalyzed esterification reaction. Butyric acid, being a short-chain polar acid, concentrates in the microaqueous layer and causes a pH drop in the enzyme microenvironment leading to enzyme inactivation. Butyric acid binds to acyl-enzyme complex unproductively to yield a dead-end intermediate that can no longer give rise to an ester. High concentration of butyric acid gave rise to inactivation of the biocatalyst in addition to dead-end inhibition.
已对脂肪酶催化丁酸与异戊醇酯化反应的动力学进行了研究。该反应速率可用米氏方程来描述，其机制为乒乓双底物机制，且两种底物均存在竞争性抑制作用。未检测到任何可能影响动力学的显著扩散限制的证据。表观动力学参数的值计算如下：V(max)=11.72微摩尔/分钟/毫克；K(M, 酸)=0.00303摩尔/升；K(M, 醇)=0.00306摩尔/升；K(i, 酸)=1.05摩尔/升；K(i, 醇)=6.55摩尔/升。本研究表明在脂肪酶催化的酯化反应中丁酸存在竞争性酶抑制作用。丁酸作为一种短链极性酸，集中在微水层中，导致酶微环境的pH值下降，从而导致酶失活。丁酸与酰基酶复合物非生产性结合，产生一个不再能生成酯的终产物中间体。除了终产物抑制外，高浓度的丁酸还导致生物催化剂失活。
