Troponin in both smooth and striated muscles of Ascidian Ciona intestinalis functions as a Ca2+-dependent accelerator of actin−myosin interaction.

Troponin, a Ca2+-dependent regulator of muscle contraction, acts as an inhibitor of the actin−myosin interaction in the absence of Ca2+ during contraction in vertebrate striated muscle. However, variation has been observed in the mode of troponin-dependent regulation among the animals belonging to Protochordata, the taxon most closely related to Vertebrata. Although troponin in striated muscle of a cephalochordate amphioxus functions as an inhibitor in the absence of Ca2+ as in vertebrates [Dennisson, J.

Functional characteristics of amphioxus troponin in regulation of muscle contraction.

Troponin regulates contraction of vertebrate striated muscle in a Ca(2+)-dependent manner. More specifically, it acts as an inhibitor of actin-myosin interaction in the absence of Ca(2+) during contraction. In vertebrates, this regulatory mechanism is unlike that in some less highly derived taxa.

X-ray structures, photophysical characterization, and computational analysis of geometrically constrained copper(I)--phenanthroline complexes.

A series of three geometrically constrained C(2)-symmetric Cu(I) mono-phenanthroline complexes were characterized by X-ray structural analysis, and their photophysical properties were investigated by absorption and emission spectroscopy. Visible light excitation yielded metal-to-ligand charge-transfer (MLCT) excited states with luminescence lifetimes up to 155 ns. Ultrafast transient absorption spectroscopy provided further insights into the excited-state dynamics and suggests for all three complexes the formation of a phenanthroline radical anion.