Chymotrypsinogen titration

The resonances of protons in hydrogen bonds may be shifted downfield to such an extent that they may be observed in H20 solutions. The proton between Asp-102 and His-57 in chymotrypsinogen, chymotrypsin, and other serine proteases has been located and its resonance found to titrate with a pKa of 7.518 (although the pKa is for the dissociation of the proton on the other nitnjjgen of the imidazole ring). ... 

It may be noted finally that more classes of titratable groups than have been discussed so far may be discernible. Figure 4 is a particularly striking example. It shows that the phenolic groups of chymotrypsinogen may, simply on inspection, be divided into three separate classes. 

Titration curves for bovine a-chymotrypsinogen have been determined under a variety of conditions by Wilcox (1961). The results are summarized in Table IX. The spectrophotometric titration of the phenolic groups is shown in Fig. 4. 

The titration curve of native chymotrypsinogen is reversible between pH 2.5 and pH 11. Analysis by the methods of Section VI shows that the neutral pH region can be described by a single intrinsic dissociation constant for all three groups which titrate in the region, together with a w... 

Havsteen and Hess (1962) have studied the titration of the phenolic groups of a-chymotrypsin and of its diisopropylphosphoryl (DIP) derivative. The result is similar to that observed with chymotrypsinogen (Fig. 4) in that only two of the four groups are available for titration in the native protein, as well as in the DIP derivative. The data do not have sufficient precision to determine whether the two titratable groups have different pK s, as they do in chymotrypsinogen, but the wide spread of the titration curve suggests that they do. 

J. L. Markley and I. B. Ibanez (1978), Zymogen activation in serine proteinases. Proton magnetic resonance pH titration studies of the two histidines of bovine chymotrypsinogen A and chymotrypsin Aa. Biochemistry 17, 4627-4639. 

Fig. 7. Summary of P-NMR titration data of diisopropylphosphoryl derivatives of serine proteinases. The arrows represent the extent of titration shuts and the numbers indicate pA , values. Abbreviations DIP, diisopropylphosphoryl BCtg, bovine chymotrypsinogen A BTg, bovine trypsinogen PTg, porcine trypsinogen BCtr , bovine chymotrypsin A BTr, bovine trypsin PTr, porcine trypsin a-LP, a-lytic proteinase. From Porcubcu et al. (1979). Copyright 1979 American Chemical Society.

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