During the same decade, a sulfonamide-resistant CA activity was discovered in male rat liver homogenates Citation17, Citation18 and in chicken muscle tissue Citation19. During 1970s, the amino acid sequences and X-ray crystal structures were reported for both human CAI and CAII Citation12–16. The A isozyme, identical to the B isoforms, and the C enzyme were later designated as CAI and CAII, respectively, and this is still their acronyms. The A and B isoforms, in fact, showed an indistinguishable amino acid composition, while the C isoform was characterized by a unique amino acid composition as well as a higher catalytic activity for carbon dioxide hydration when compared with the A and B isoforms Citation11. It should be mentioned that this nomenclature is no longer used for decades. Human erythrocyte revealed three CA isoforms on basis of the electrophoretic analysis, which were designated as the A, B and C isoforms Citation5–10. Initially, the α-CA was purified from bovine erythrocytes Citation4.
This is one of the reasons that promted us to evaluate the purification and characterization methods of the α-CA family, since such a review article has not yet been published.
The CAs have been the targets of drug development for the treatments of glaucoma, obesity, osteoporosis, epilepsy, high altitude sickness, as well as cancer Citation1–3. All these isoforms have been described in detail Citation1, Citation2. They also differ in their subcellular localization: CAI, CAII, CAIII, CAVII, CA VIII, CA X, CA XI and CA XIII are found in cytoplasm CAIV, IX, XII, XIV and XV are membrane-bound forms two mitochondrial forms, CAVA and VB and CAVI is a secretory form. Nowadays, 16 isoforms are known in vertebrates, all belongings to the α class. Mammalian erythrocytes, where CA was originally discovered, contain two distinct isozymes (CAI and CAII) differing in their catalytic activities. In plants, CAs are involved in the photosynthetic fixation of CO 2. CA plays an important role in many physiologic processes, such as, for example, respiration, by facilitating the transport of CO 2 from metabolizing tissues to lungs. Inhibition studies of CAs identified in the genome of the aforementioned organisms might lead to the discovery of innovative drugs with a novel mechanism of action.Ĭarbonic anhydrase (CA, EC 4.2.1.1.) is a zinc-containing metalloenzyme that is widespread in nature and catalyzes the reversible hydration of CO 2 to and H +. Recently, it was discovered an involvement of CAs in cancerogenesis as well as infection caused by pathogenic agents such as bacteria, fungi and protozoa. α-CAs possess important application in medicine (as many human α-CA isoforms are drug targets) as well as biotechnological processes, in which the enzymes are ultimately used for CO 2 capture in order to mitigate the global warming effects due to greenhouse gases.
Starting from the manuscripts published in the 1930s on the isolation and purification of α-CAs from blood and other tissues, and ending with the recent discovery of the last genetic family in protozoa, the η-CAs, considered for long time an α-CA, we present historically the numerous and different procedures which were employed for obtaining these catalysts in pure form. Six genetic families (α-, β-, γ-, δ-, ζ- and η-CAs) all know to date, all encoding such enzymes in organisms widely distributed over the phylogenetic tree. In this paper, we reviewed the purification and characterization methods of the α-carbonic anhydrase (CA, EC 4.2.1.1) class.
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