Tyrosine optical rotation

Nelson and Hummel 351) made a careful investigation of the urea transition near pH 7. Their absorbance difference spectra clearly show changes in the environment of phenylalanine as well as tyrosine residues. The optical rotation changes occur in the same range of urea concentrations. The loss of enzymic activity (U>p) is biphasic. At low urea con-... 

The stereochemistry of 43 was established to be S by comparing the optical rotation of an authentic sample derived from (R)-//-tyrosine hydrochloride with //-tyrosine hydrochloride isolated from edeine A and B [62], Incubation experiments with [lsN]tyrosine revealed that the [15N]amino group in //-tyrosine is lost, suggesting a reaction mechanism similar to that of an ammonia lyase [62]. This finding is supported by further incubation experiments with (2RS,3R)-[3-3H]tyrosine and (2RS,3S)-[ 3-3H tyrosine in combination with (2RS)-[3-14C]tyrosine. Determination of the 3H/14C ratios of the isolated //-tyrosine 43 leads to the conclusion that the pro-3 S hydrogen is lost in the course of the reaction whereas the pro-3R hydrogen is retained (Scheme 1.6.14). A similar incubation experiment with (2S)-[2-3H]tyrosine proceeds with a loss of most of the tritium label from C2. 

Figure 4.6-13 Optical rotation q recorded as outlined in Fig. 4.6-12 Spectra of two differently concentrated solutions of S-tyrosine-methylester in the nematic mixture EBBA/MBBA (equimolar mixture of N-(p-ethoxybenzylidene)-p - -butylaniline and its methoxy analogue 2 of Table 4.6-1 Riedel-de Haen), left RCE (molar fraction x fa 0.024) related to the selective reflection band indicating pitch and handedness of the. structure, thus characterizing the chirality of the solute molecules by the helical twisting power right Sequence of ACE (,v se 0.0024, therefore the RCE should occur around 200 cm ) each of which indicates the induced handedness and therefore, discriminates enantiomers (Koite, 1978).

In 1958 we had reported that in contrast to most globular proteins, the specific optical rotation, [a], the hydrodynamic properties, and, most of all, the enzymic activity of pepsin remain unaltered if the protein is dissolved in concentrated urea solution or in guanidine hydrochloride, or if the solution is heated to 60°C. However, if the temperature is raised to 70°C., the rotatory dispersion constant, Xc, increases from 216 to 236 m/z (15, 18). Although hydrogen bonds of the type C = O. . . H — N and those involving the phenolic hydroxyls of tyrosine and the carboxylate ions of the acidic amino acid residues—i.e.,... 

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