Siffert W, Gros G
Biochem J. 1982 Sep 1;205(3):559-66. doi: 10.1042/bj2050559.
We investigated the activity of carbonic anhydrase in blood-free perfused white skeletal muscles of the rabbit. Carbonic anhydrase activities were measured in supernatants and in Triton extracts of the particulate fractions of white-skeletal-muscle homogenate by using a rapid-reaction stopped-flow apparatus equipped with a pH electrode. An average carbonic anhydrase concentration of about 0.5 microM was determined for white skeletal muscle. This concentration is about 1% of that inside the erythrocyte. Some 85% of the muscle enzyme was found in the homogenate supernatant, and only 15% appeared to be associated with membranes and organelles. White-skeletal-muscle carbonic anhydrase was characterized in terms of its Michaelis constant and catalytic-centre activity (turnover number) for CO2 and its inhibition constant towards ethoxzolamide. These properties were identical with those of the rabbit erythrocyte carbonic anhydrase C, suggesting that a type-C enzyme is present in white skeletal muscle. Affinity chromatography of muscle supernatant and of lysed erythrocytes showed that, whereas rabbit erythrocytes contain about equal amounts of carbonic anhydrase isoenzymes B and C, the B isoenzyme is practically absent from white skeletal muscle. Similarly, ethoxzolamide-inhibition curves suggested that white skeletal muscle contains no carbonic anhydrase A. It is concluded that white skeletal muscle contains essentially one carbonic anhydrase isoenzyme, the C form, most of which is probably of cytosolic origin.
我们研究了兔白骨骼肌无血灌注时碳酸酐酶的活性。通过使用配备pH电极的快速反应停流装置，测定了白骨骼肌匀浆颗粒部分的上清液和Triton提取物中的碳酸酐酶活性。测定出白骨骼肌中碳酸酐酶的平均浓度约为0.5微摩尔/升。该浓度约为红细胞内浓度的1%。在匀浆上清液中发现约85%的肌肉酶，仅有15%似乎与膜和细胞器相关。根据其对二氧化碳的米氏常数、催化中心活性（转换数）及其对乙氧唑胺的抑制常数对白骨骼肌碳酸酐酶进行了表征。这些特性与兔红细胞碳酸酐酶C相同，表明白骨骼肌中存在C型酶。对肌肉上清液和裂解红细胞进行亲和层析显示，兔红细胞中碳酸酐酶同工酶B和C含量大致相等，而白骨骼肌中几乎不存在B同工酶。同样，乙氧唑胺抑制曲线表明白骨骼肌中不存在碳酸酐酶A。结论是白骨骼肌基本上只含有一种碳酸酐酶同工酶，即C型，其中大部分可能来源于胞质。
