Lewis C A, Wolfenden R
Biochemistry. 1977 Nov 1;16(22):4886-90. doi: 10.1021/bi00641a022.
Equilibrium constants for hydration of ketones, in dilute D2O solution at 34 degrees C, observed by proton magnetic resonance under conditions of slow exchange, were acetone 0.002, chloroacetone 0.08, 1,3-dichloroacetone 4.17, bromoacetone 0.07, and 1,3-dibromoacetone (an inhibitor of papain) 1.85. Neither acetamidoacetone nor N,N-diacetylaminoacetone showed evidence of appreciable hydration in dilute aqueous solution, nor was any hydrate detectable in solutions of tosylglycine chloromethyl ketone. Substitution of acetaldehyde with acylamido substituents, as in several potent reversible inhibitors of papain, was found to enhance its equilibrium constant for covalent hydration by an order of magnitude; these inhibitors are about 90% hydrated in dilute aqueous solution, and their affinity for proteases may have been underestimated accordingly. The effects of deuterium substitution at C-1 of acetaldehyde, on equilibrium addition of oxygen and sulfur nucleophiles, are substantial and vary with the nature of the nucleophile. These isotope effects may be useful as a mean of distinguishing between alternative structures of complexes formed between enzymes and aldehydes.
在34℃的稀重水溶液中，通过质子磁共振在缓慢交换条件下观察到的酮水合平衡常数，丙酮为0.002，氯丙酮为0.08，1,3 - 二氯丙酮为4.17，溴丙酮为0.07，以及1,3 - 二溴丙酮（木瓜蛋白酶抑制剂）为1.85。在稀水溶液中，乙酰氨基丙酮和N，N - 二乙酰氨基丙酮均未显示出明显水合的迹象，在甲苯磺酰甘氨酸氯甲基酮溶液中也未检测到任何水合物。发现用酰氨基取代基取代乙醛，如在几种有效的木瓜蛋白酶可逆抑制剂中那样，可使其共价水合的平衡常数提高一个数量级；这些抑制剂在稀水溶液中约90%水合，因此它们对蛋白酶的亲和力可能被低估了。乙醛C - 1位的氘取代对氧和硫亲核试剂的平衡加成的影响很大，并且随亲核试剂的性质而变化。这些同位素效应可作为区分酶与醛形成的复合物的不同结构的一种手段。
