Carbonic anhydrase species differences

Zinc is involved in many biochemical functions. In 1940 Keilin and Mann (11) reported for the first time that carbonic anhydrase was a zinc metalloenzyme. Over the next 20 years, only five additional zinc metallo-enzymes were identified, but in the past 15 years, the total number of related enzymes from different species is more than 70 (12). Besides its role in the functions of enzymes, recently it has been shown that zinc may be involved in maintenance of structures of polynucleotides, apoenzymes, and biomembranes (13,14). 

Based on these findings, extinction coefficients for the various conformational species were measured under the following conditions OM urea for native hCAB, 8M urea for the denatured conformer, incubation in 5M urea for 90-120 minutes to estimate the extinction coefficient for X, and incubation in SM urea for an extended period of time (2 3 weeks was used in this study) to determine the extinction coefficient for conformer I. Initial extinction coefficients evaluations at 238 nm and 292 nm for the various human carbonic anhydrase B conformers were determined in O.IM Tris-HCl (pH=7.45) at 23 C. The results are presented in Table 2. It is evident that while there is a substantial (-25-35%) difference in extinction coefficients between the native and denatured states, the intermediate conformations X and I could not be separated spectroscopically, and therefore, UV absorbance cannot be used to determine the concentration of species X and I separately. Instead, the overall concentration of intermediate species, Z where [Z]=[X]+[q, was monitored over the course of a refolding experiment... 

Les.), and Couceiro, de Almeida, and Freire (1953) have localized it histo-chemically in the electrical tissue of Electwphorus electricus L. The distribution of carbonic anhydrase in several tissues of two teleosts and its inhibition in vivo by the sulfonamides have been investigated by Maetz (1953a,b). The presence of cathepsin in the stomachs of various animals including pike and trout has been established by Buchs (1954). A new advance has also been made in the comparative study of pepsin. This enzyme, previously crystallized from salmon (Norris and Elam, 1940), halibut (Eriksen, 1943), and shark (Sprissler, 1942), has now been crystallized from three species of tuna (Norris and Mathies, 1953). These interesting researches have shown that fish pepsins differ in crystal structure, amino acid composition, and specificity from swine or bovine pepsins and show a closer relationship to one another. As pointed out by Velick and Udenfriend (1953), specificity requirements toward substrates are less exacting with extracellular enzymes. 

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