O'Connor J, Wallace R G
Eur J Biochem. 1984 Jun 1;141(2):379-83. doi: 10.1111/j.1432-1033.1984.tb08202.x.
The pseudo-first-order rate constants of hydrolysis of p-nitrophenylacetate, catalyzed by human milk lipase, have been measured in solutions of 0.01 mol dm-3 Bistris(2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)-propane-1,3 -diol) buffer at 310.5 K, containing a range of concentrations of sodium taurocholate and sodium cholate, at pH 8.00 and of sodium cholate at pH 6.5. The effect of pH on the activity of the enzyme has been investigated and the stimulation factors of taurocholate and cholate ions and of cholic acid have been calculated to be equal to 5.3, 3.7 and 10.7, respectively. The essential residues for catalytic activity of the enzyme have ionization constants equal to 6.45-6.46 for pK1 and 8.33-8.40 for pK2. The former value is attributed to the presence of a histidine imidazolium group but the identity of the residue leading to pK2 is not proven.
在310.5 K下，于0.01 mol dm⁻³双（2-[双（2-羟乙基）氨基]-2-（羟甲基）丙烷-1,3-二醇）缓冲液中，测定了人乳脂肪酶催化对硝基苯乙酸酯水解的准一级速率常数，该缓冲液含有一系列不同浓度的牛磺胆酸钠和胆酸钠，pH为8.00，以及pH为6.5时的胆酸钠。研究了pH对该酶活性的影响，计算得出牛磺胆酸根离子、胆酸根离子和胆酸的刺激因子分别等于5.3、3.7和10.7。该酶催化活性的必需残基的电离常数，pK1为6.45 - 6.46，pK2为8.33 - 8.40。前一个值归因于存在组氨酸咪唑鎓基团，但导致pK2的残基身份尚未得到证实。
