The screw-sense-selective polymerization of isocyanides has been attained by the catalysis of dinuclear transition metal complex Cl(PR3)2PdC≡CPt(PR3)2Cl 2 using a block-copolymerization technique. (l)-and (d)-3-Menthoxycarbonylphenyl isocyanides are polymerized to give single-handed helical polymers 5(l)n and 5(d)n, respectively, which exhibit a large optical rotation arising from the helical chirality. Oligomer complexes, prepared from the reaction of 2 with the chiral isocyanides, effectively initiate the screw-sense selective polymerization of achiral isocyanides like 3, 5-di(propoxycarbonyl)phenyl isocyanide to produce single-handed helical polymers which preserve the screw sense of the initiators, although sterically smaller isocyanides such as 4-butyl- and 3-propoxycarbonylphenyl isocyanides are polymerized with gradual loss of the screw-sense selectivity in propagation steps. This short review focuses on the recent development of helical polymers such as poly(alkyne)s and poly(isocyanide)s which are synthesized by the catalysis of well-defined organotransition metal complexes.
Phosphorylation site responsible for the regulation of smooth muscle myosin was mapped using a polyclonal antibody against a phosphorylated hendecapeptide corresponding to the amino acid sequence around Ser-19 in the regulatory light chain. Phosphorylated myosin mixed with the antibody was rotary-shadowed and was examined by electron microscopy. The antibody binding site was located in the head portion of myosin and the average distance from the head-rod junction was about 3nm toward the tip of myosin head. The results indicate that the phosphorylated Ser-19 in regulatory light chain is a little more extended toward the adjacent essential light chain in reference to the resolved N-terminal residues of the regulatory light chain in the three dimensional structure of myosin heads from other sources, in which the structure of the N-terminal portions homologous to the phosphorylated Ser-19 was not resolved (Rayment, I. et al. (1993) Science 261, 50-58; Xie, X. et al. (1994) Nature 368, 306-312). Intramolecular interaction through the introduced phosphoryl group may be the primary results in the regulatory light chain which releases the motor domain from its suppressed state.