Metal-ligand interactions in the Ca"-binding sites of pike parvalbumin (PI = 4.10) have been examined by Fourier-transform infrared spectroscopy. The region of the COO-antisymmetric stretch provides useful information on the types of coordination of the COO-groups to the metal ions in the Mg"-, Mn"-, and Ca"-bound forms. In the spectrum of the Ca*'-bound form, two bands are observed at 1,582 and 1,553 cm-', whereas, in the spectra of the Me-and Mn"-bound forms, bands are observed only in the region around 1,582 cm-' and no band is found in the region around 1,553 cm-'. The 1,553-cm-' band of the Ca*'-bound form reflects the bidentate coordination of the COO-groups of both Glu-62 in the CD site and Glu-101 in the EF site to the Ca" ions, which has been made clear by X-ray analysis as a feature of the Ca"-bound form. Absence of such a band in the spectrum of the Mn"-bound form is consistent with the X-ray structure of this form where both of the two COO-groups are unidentate. These unidentate COO-groups of Glu-62 and Glu-101 in the Mn"-bound form seem to give rise to a band at 1,577-1,574 cm-'. The spectrum of the Mg"-bound form is also consistent with the 'pseudo-bridging' coordination of the COO-group of Glu-101 reported in the X-ray structure of a form where the Mg2+ ion occupies only the EF site, and the same spectrum is further indicative of the 'pseudo-bridging' coordination of the COOgroup of Glu-62.

A chiral substituted acetylene, (s)-2-octyl propiolate, was stereoregularly polymerized using a catalyst, [Rh(nbd)Cl]2, at 40 °C in methanol to give the corresponding helical polymer, Ps2OcP. The changes of (1)H and (13)C NMR spectra in line shapes and splitting patterns were consistently interpreted in terms of restricted rotation around the ester O-*C bond, ~O-*C(ε)H(ε)(R)~, R = a branched CH(ε)3 in the ester side chains rather than the helix inversion with the aid of a 3-site jump model. Three peaks due to the branched methyl H(ε) proton and its C(η) carbon observed at 0 °C suggested the formation of three rotamers called A, B, and C, based on the presence of the contracted helix and stretched helix forms that have an intrinsic helical pitch. Furthermore, an accordion-like helix oscillation (HELIOS) along the main chain axis was proposed to explain the temperature dependence spectral changes observed in (1)H and (13)C NMR, UV-vis, and circular dicromism (CD) spectra. The temperature dependence UV-vis and CD spectra of Ps2OcP corroborate the presence of contracted and stretched one-handed helix sense polymers in solution in which the helical pitches and their persistence lengths depend on the temperature.

The effect of hydration on the structure and dynamics ofBombyx morisilk was clarified at the molecular level.

The 400-MHz 1H nuclear magnetic resonance (NMR) studies were carried out on the Ca2+-induced conformational change of calmodulins (CaM's) isolated from scallop testis and pig brain. The resonances were found to be classified approximately into three groups. The resonances of group I, which are perturbed by the binding of Ca2+ to the high-affinity sites, include those of tyrosine-138, epsilon-trimethyllysine-115, histidine-107, tyrosine-99, etc. The previous assignments for tyrosine- (Tyr) 138 [Seamon, K. B. (1980) Biochemistry 19, 207] were corrected. The resonances of group II, which are affected by the binding of Ca2+ to the low-affinity sites, include those of a phenylalanine (Phe), a high field shifted methyl, and a low field shifted alpha-methine. Group III (related to the binding of Ca2+ to both the high-and low-affinity sites) includes the resonances of a Phe, a high field shifted methyl, and threonine-143. It is concluded that sites III and IV are the high-affinity sites. The off-rate of Ca2+ from the high-affinity sites is slower than 50 s-1 while the off-rate from the low-affinity sites is faster than 600 s-1. In the Ca2+-free state, there exists a hydrophobic region containing three phenylalanine (probably Phe-89, Phe-92, and Phe-141), a valine, and an isoleucine in the vicinity of sites III and IV. Tyr-138 is distant from these amino acids. Upon binding of Ca2+ to the high-affinity sites, one of the Phe residues and the valine approach Tyr-138. Similar structural changes were observed between CaM and troponin C when Ca2+ ions are bound to the high-affinity sites. CaM changes in a somewhat different way from troponin C when Ca2+ ions are bound to the low-affinity sites.