Optical Rotatory Dispersion and Circular Dichroism of
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چکیده
Studies of optical rotatory dispersion (ORD) and circular dichroism (CD) are reported on pepsinogen, carbamyl-, and succinylpepsinogen. From the ORD measurements in the wave length range of 600 to 300 rnp as functions of urea, temperature, and pH, it was shown that the macromolecular conformation of the three proteins differs markedly. On replacing the e-NH2 groups of the lysine residues of pepsinogen by non-polar groups (carbamylpepsinogen) or acidic side chains (succinylpepsinogen), the electrostatic side chain interaction between the basic residues and some dicarboxylic acids which stabilizes pepsinogen is abolished. With all three proteins the changes in [n], particularly when measured as function of pH, parallel those of the specific rotation, [(Yl366. The ORD spectra below 300 rnp show several peaks and troughs. The principal trough of the three proteins in phosphate buffer of pH 7.7 and 0.1 ionic strength is at 227 rnp and is shifted to 230 rnp if the temperature is raised or the pH of the solutions is altered. The positive maximum is at 202 rnp for pepsinogen, at 200 rnp for carbamylpepsinogen, and at 195 rnp for succinylpepsinogen. The ORD spectra above 260 rnp show a trough at 278 mp, most likely involving the aromatic side chains. These patterns are very different from those characteristic for a-helical structures. The CD spectra of the three proteins at pH 7.7 are characterized by a strong negative band at 212, 205, and 202 rnp for pepsinogen, the carbamyl, and succinyl derivative, respectively. These are displaced to lower wave lengths in the alkaline pH range. The positive CD band of pepsinogen in the phosphate buffer of pH 7.7 is at 193 m+ Above 250 mp, dichroic bands were recorded at 255, 264, 278, 292, and 300 ml*. The band at 278 rnp is pH-dependent and was assigned to the aromatic amino acid residues. As the pH is raised above pH 10.0, the band passes through zero and changes sign. ORD spectra have been calculated from the CD data for
منابع مشابه
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