Purification, Molecular Properties and Ontogeny of Carbonic Anhydrase Isozymes. Evidence for A, B and C Isozymes in Avian and Mammalian Tissues

Abstract

Carbonic anhydrase A from sheep and chicken red skeletal muscles and carbonic anhydrases B and C from chicken intestine and red cells respectively have been isolated in a high state of purity by affinity chromatography. The subunit and native molecular weights of sheep carbonic anhydrase A determined by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and Sephadex gel filtration respectively were both approximately 34000. In contrast, carbonic anhydrases A, B and C from chicken exhibited a molecular weight determined by sodium dodecyl sulphate electrophoresis of 30000. The amino acid composition of sheep muscle carbonic anhydrase A was distinct from the B and C isozymes, particularly in basic amino acid content, which was significantly higher for the A isozyme (38 cJ: 24-291mol). The zinc content of sheep carbonic anhydrase A was found to be 0.81 g atom Zn/mol. The specific activities of chicken carbonic anhydrase isozyme differed significantly according to the ratio A:B:C = 1 :6:47. In addition, these isozymes differed in their affinities for sulphonamide. Chicken carbonic anhydrase A was approximately 100 times less sensitive to acetazolamide inhibition than the chicken C isozyme. Ontogenetic studies in cats showed carbonic anhydrase C to be the only form of the enzyme present in mid-term fetal animals, with carbonic anhydrase A appearing in muscle in the late stages, and carbonic anhydrase B appearing in caecum within 2 days of birth.The evidence is consistent with previous proposals for a third locus encoding carbonic anhydrase in mammalian and avian species. This isozyme (A) is a monomeric, zinc metalloenzyme, which differs from the extensively studied B and C isozymes of carbonic anhydrase in terms of catalytic efficiency, amino acid composition, molecular weight (in sheep), time of ontogenic appearance, sulphonamide inhibition and tissue distribution.

Low-dose Acetazolamide Does Affect Respiratory Muscle Function in Spontaneously Breathing Anesthetized Rabbits

“…Studying the effect of acetazolamide at the (neuro)muscular level would be important for at least two reasons. First, muscle cells contain several isoforms of carbonic anhydrase and inhibition of these may affect the efficiency of the excitationcontraction mechanism (11)(12)(13)(14)(15). Second, patients with COPD may suffer from severe peripheral muscle weakness, particularly when they are treated with steroids (16).…”

Deficiency of carbonic anhydrase in the vasculature of rabbit kidneys.

“…In contrast to the pulmonary epithelium, which seems devoid of c.a. (4,10), and the muscle cells, which contain a very inactive form of the enzyme (41)(42)(43), there is abundant c.a. activity associated with both the cytoplasm and membranes of many renal tubular cells (32)(33)(34)(35)(36).…”

Testosterone‐induced, sulfonamide‐resistant carbonic anhydrase isozyme of rat liver is indistinguishable from skeletal muscle carbonic anhydrase III

“…In contrast, MUP's (which may be evolutionarily related to a2,-globulin) are excreted by both adult male and female mice, although males excrete higher levels. In this respect, it is of interest that both adult male and female mice appear to exhibit similar levels of CA III in their livers [2].…”