Abstract
Abstract The circular dichroism of ribonuclease A, ribonuclease S, S-protein, S-peptide, and ribonuclease S' has been measured in aqueous solutions in the 215 to 300 mµ region. The circular dichroism spectra of ribonuclease A and ribonuclease S are virtually identical; that of ribonuclease S' is similar but lacks a positive peak at 240 mµ. S-protein exhibits a more negative ellipticity between 232 and 265 mµ. Upon addition of S-peptide to S-protein, the circular dichroism in this region becomes less negative. These differences are tentatively attributed to changes in the contribution of a tyrosyl residue near 240 mµ. Ribonuclease A and ribonuclease S exhibit no positive 240 mµ circular dichroism maximum in solutions below pH 2 and 3.5, respectively; this pH dependence suggests that a side chain carboxylic acid residue interaction occurs.
Highlights
The three-dimensional crystalline structure of RNase-S is virtually identical with that of RNase-A except for the region of the molecule adjoining residues 20 and 21 where a peptide bond is broken in RNase-S
In an attempt to study the conformational changes associated with the formation of RNase-S’, we have studied the circular dichroism of RNase-A, RNase-S, S-protein, and S-peptide, as well as RNase-S’
RNase-A has been reported to exhibit a small positive CD maximum near 240 rnp [5, 22]. This maximum was initially attributed to either a tyrosyl contribution or a disulfide absorption, it appears more likely that it is of tyrosyl origin, since it has been observed both in proteins [23] and in peptides [24] which contain tyrosine residues but no disulfide bonds
Summary
The three-dimensional crystalline structure of RNase-S is virtually identical with that of RNase-A except for the region of the molecule adjoining residues 20 and 21 where a peptide bond is broken in RNase-S. Indicated that, upon addition of S-peptide to S-protein, the number of “abnormal” tyrosines in the latter increases from 2 to 3 (lo), i.e. to the same number found in RNase-A [18]. RNase-S’ exhibits a negative maximum in the same spectral region.
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