Raghavendra M P, Kumar Parigi Ramesh, Prakash V
Dept. of Protein Chemistry and Technology, Central Food Technological Research Inst., Mysore 570 020, India.
J Food Sci. 2007 Oct;72(8):E412-9. doi: 10.1111/j.1750-3841.2007.00488.x.
Rice bran is a byproduct obtained from the rice milling industry, and to arrest lipolysis caused by lipolytic enzyme, rice bran lipase (RBL) was inactivated by inhibitors such as polyphenols. This study describes the inhibition and interaction of enzyme with chlorogenic acid (CGA) and caffeic acid (CA). The inhibition of the enzyme was competitive in nature in both CGA and CA. The inhibition constant K(i) of the reaction was found to be 1.8 and 1.5 muM for CGA and CA, respectively. Fluorescence emission measurements indicated a decrease in the fluorescence emission intensity and a red shift in the emission maximum as these ligands concentrations are increased, indicating the minor changes in the tryptophan environment and the effect of binding that is stronger in the case of CA compared to CGA with RBL. Far UV-circular dichroic data suggest that there are no significant changes in the conformation of the enzyme as a result of binding of CGA or CA. The instability of the enzyme in the presence of these polyphenols has been indicated by decrease in apparent thermal transition temperatures of the enzyme from a control value of 60 degrees C as revealed by thermal denaturation measurements. These results demonstrate that both CGA and CA are inhibitors of RBL and bind to the enzyme through both hydrogen and hydrophobic interaction in bringing about inhibition with minor structural alterations. These inactivation phenomena of polyphenols that act as inhibitors on RBL can be utilized to prevent oxidation of the rice bran oil.
米糠是稻米碾磨工业的副产品，为抑制脂肪分解酶引起的脂解作用，米糠脂肪酶（RBL）会被多酚等抑制剂失活。本研究描述了该酶与绿原酸（CGA）和咖啡酸（CA）的抑制作用及相互作用。在CGA和CA中，该酶的抑制作用本质上均为竞争性抑制。反应的抑制常数K(i)对于CGA和CA分别为1.8和1.5 μM。荧光发射测量表明，随着这些配体浓度增加，荧光发射强度降低且发射最大值出现红移，这表明色氨酸环境有微小变化，且与RBL结合时CA的结合作用比CGA更强。远紫外圆二色性数据表明，CGA或CA的结合并未导致该酶的构象发生显著变化。热变性测量显示，在这些多酚存在下，该酶的表观热转变温度从对照值60℃下降，这表明了酶的不稳定性。这些结果表明，CGA和CA均为RBL的抑制剂，它们通过氢键和疏水相互作用与酶结合，从而在结构变化较小的情况下实现抑制作用。这些作为RBL抑制剂的多酚的失活现象可用于防止米糠油氧化。
