Based on pigment composition analysis of a series of photosystem (PS) 1-type reaction centers( RCs), we have proposed a novel hypothesis that chlorophyll (Chl) a' and bacteriochlorophyll (BChl) g', the epimers of Chl a and BChl g, constitute the primary electron donors of PS1 and heliobacterial RCs, respectively. Interestingly, PS1-type RCs are devoid of (bacterio) pheophytin but have Chl a-like pigments as primary electron acceptors, and PS2-type RCs do not possess prime-type Chls at all.
A number of self-defense peptides have been isolated in the animal kingdom. They selectively kill microorganisms by permeabilizing the cell membranes, whereas they do not show any significant cytotoxicity for mammalian cells. Magainin 2 from Xenopus skin was found to form a peptide-lipid supramolecular complex pore in the membrane, followed by peptide internalization, simultaneously dissipating the transmembrane potential and the lipid asymmetry. Tachyplesin I from Tachypleus also translocates across the membrane by forming a pore. The membrane selectivity of these peptides is closely related to their affinity for the lipids constituting the membrane surface.
In contrast to vertebrate phototransduction, invertebrate one remains unclear. This review gives a very brief and bold outline of invertebrate phototransduction, lying stress on the second messenger and light-sensitive channel that mediates the photroreceptor potential. Both IP3/Ca2+ and cGMP are the main candidates for the second messenger. The cGMP would be involved in gating the light-sensitive channels of most of the photoreceptive cells, irrespective of vertebrate and invertebrate, while the IP3/Ca2+ be limited to some of invertebrates.
The low force actomyosin complex, formed prior to force generation in skeletal muscle, has characteristics distinct from those of conventional weak- or strong-binding complexes and therefore constitutes a third class of intermediate in the ATPase reaction. Its dual strain sensitivity enables the muscle to resist an externally applied stretch by isomerizing to a forcesupporting form, while reducing excessive energy consumption during shortening by limiting the number of myosin molecules which enter the force-generating event.