The proteolytic degradation of normal and variant human carbonic anhydrase isozymes by alpha-chymotrypsin

Effect of single amino acid substitutions on the protease susceptibility of tryptophan synthase alpha subunit

In order to explore the correlation between protease susceptibility and conformational stability of a protein, the proteolytic degradation by trypsin, subtilisin and pronase P of the wild-type alpha subunit of tryptophan synthase from Escherichia coli and of its two mutant proteins was studied by measuring circular dichroism at 222 nm at various pH values at 37 degrees C. The mutant proteins are substituted by Gln or Met in place of Glu at position 49. The single amino acid substitutions at position 49 significantly affected susceptibility of this protein to the three proteases. Dependence of protease susceptibility of the wild-type and the two mutant proteins on pH was characteristic of each protein and similar for the three proteases. Comparison of the present results with the conformational stabilities of the three proteins previously measured shows that the order of resistance to the proteases among the three proteins coincides with the order of the values of unfolding Gibbs energy change, suggesting that protein degradation depends upon the conformational stability of a protein.

Genetic variation in the carbonic anhydrase isozymes of macaque monkeys. IV. Degradation by heat and proteolysis of normal and variant carbonic anhydrase isozymes of Macaca nemestrina

Studies were undertaken on the heat denaturation and proteolytic degradation by alpha-chymotrypsin of the normal red cell carbonic anhydrase isozyme, CA II, and two electrophoretic variants of carbonic anhydrase I, CA Ia and CA Ib, of the pigtail macaque. The heat degradation results showed a difference of about 40-fold in the rate constants between CA Ia and CA Ib, which is due to the marked thermostability of CA Ib compared to CA Ia. The enthalpies and entropies of activation were calculated from the heat denaturation constants. These values were compared, on enthalpy-entropy compensation plots, with those values previously determined for the human CA I and CA II isozymes. They were highly correlated and clearly fell into two distinct clusters, separated by about 200 kJ mol-1; one group comprising the macaque and human CA I isozymes and the other the CA II isozymes. The proteolytic degradation results showed that CA Ia is degraded about 2.5 times more rapidly than CA Ib by alpha-chymotrypsin. Thus, the characteristic 3/1 ratio of CA Ib/CA Ia in mature red cells could be accounted for by the greater susceptibility of CA Ia to degradation at some stage in red cell development.

Dissociation constants for carbonic anhydrase--sulfonamide binding by high-performance liquid chromatography

Carbonic anhydrase-azosulfonamide dissociation constants (Kd) were determined by gel filtration with high-performance liquid chromatography. By measuring the area of the elution peak at two wavelengths, Kd values were derived without having to measure a shallow trough. The procedure proved to be fast and reliable and has a general application. The dissociation constants were measured for 7-acetamido-2-(4'-sulfamylphenylazo)-1-hydroxynaphthalene-3, 6-disulfonate (Neoprontosil) complexes with carbonic anhydrase isozymes CA I, CA II, and CA III from bovine and human sources, and chicken CA III from skeletal muscle.

A chemical and enzymological comparison of the common major human erythrocyte carbonic anhydrase II, its minor component, and a new genetic variant, CA II Melbourne (237 Pro leads to His)

A new variant of human erythrocyte carbonic anhydrase II (CA II) was discovered in a single Caucasian family during routine screening of blood samples from Melbourne, Australia. The normal and variant enzymes in the heterozygous CA II mixture, as well as a minor component of the normal enzyme, were resolved by isoelectric focusing following purification by a specific affinity matrix. Specific esterase activities of all three were very similar, but quite different Michaelis-Menten constants were noted for the minor component. No differences were noted with respect to inhibition by acetazolamide, but the minor component was more sensitive to chloride inhibition. Double diffusion analysis showed the immunological identity of the normal, variant, and minor components. Both the variant CA II and the minor component were less heat stable than the normal enzyme, but all forms showed identical rates of inactivation upon dialysis against the zinc chelator pyridine dicarboxylic acid. Amino acid analyses of the whole protein and the single difference peptide were consistent with a proline to histidine substitution in the variant. This was identified as 237 Pro leads to His by a process of elimination involving direct sequencing of tryptic and cyanogen bromide peptides. The numbering is by homology with the human CA I sequence.