Skipski I A, Scott W N
Exp Eye Res. 1985 Dec;41(6):671-85. doi: 10.1016/0014-4835(85)90177-0.
Carbonic anhydrase in the toad lens is immunologically identical to the (high activity) enzyme form present in the erythrocyte. As with the erythrocyte carbonic anhydrase, electrofocusing of the freshly-extracted lens enzyme separated three variants with isoelectric points of 6.1, 5.7 and 5.4, all of which exhibited inhibition properties characteristic of the high activity type of carbonic anhydrase. No evidence of the low activity form of the enzyme was found. In contrast to the erythrocyte isoelectric variants, which are stable in vitro, the three variants of lens carbonic anhydrase exhibited progressive anodization in the course of purification and during storage, and could not be isolated in the original form. Acidification of lens carbonic anhydrase appears to be part of the in vivo aging process of the enzyme protein: the still-active enzyme from the oldest lens region--the nucleus--exhibited a considerably lower isoelectric point than the enzyme extracted from the younger, soft fibers of the lens. Although the specific activity of the carbonic anhydrase from the fibers of lens nucleus was considerably lower than the activity of the enzyme from the younger fibers, the observed modification (acidification) of the aged enzyme did not appear to affect substantially its binding properties towards acetazolamide nor the heat lability of the active protein.
蟾蜍晶状体中的碳酸酐酶在免疫学上与红细胞中存在的（高活性）酶形式相同。与红细胞碳酸酐酶一样，对新鲜提取的晶状体酶进行等电聚焦，分离出三种等电点分别为6.1、5.7和5.4的变体，所有这些变体都表现出高活性类型碳酸酐酶的抑制特性。未发现该酶低活性形式的证据。与在体外稳定的红细胞等电变体不同，晶状体碳酸酐酶的三种变体在纯化过程和储存期间表现出渐进性阳极化，无法以原始形式分离。晶状体碳酸酐酶的酸化似乎是酶蛋白体内老化过程的一部分：来自最老晶状体区域——核——的仍有活性的酶，其等电点比从晶状体较年轻、柔软纤维中提取的酶低得多。尽管晶状体核纤维中的碳酸酐酶比年轻纤维中的酶的比活性低得多，但观察到的老化酶的修饰（酸化）似乎并未实质性影响其对乙酰唑胺的结合特性，也未影响活性蛋白的热稳定性。
