Protection of chlorophyll a from photo-oxidation byβ-carotene in binary mixture of organic solvents

Zusammenfassung Das photoxytadive Ausbleichen des Chlorophylls a wird durch die Gegenwart des-Carotins gehemmt. Die Hemmwirkung des-Carotins und die Wechselwirkung zwischen Chlorophyll a und-Carotin werden vom Lösungsmittel kontrolliert.     

Haploinsufficiency of NSD1 causes Sotos syndrome

We isolated NSD1 from the 5q35 breakpoint in an individual with Sotos syndrome harboring a chromosomal translocation. We identified 1 nonsense, 3 frameshift and 20 submicroscopic deletion mutations of NSD1 among 42 individuals with sporadic cases of Sotos syndrome. The results indicate that haploinsufficiency of NSD1 is the major cause of Sotos syndrome.     

Structural basis for semaphorin signalling through the plexin receptor

Semaphorins and their receptor plexins constitute a pleiotropic cell-signalling system that is used in a wide variety of biological processes, and both protein families have been implicated in numerous human diseases. The binding of soluble or membrane-anchored semaphorins to the membrane-distal region of the plexin ectodomain activates plexin's intrinsic GTPase-activating protein (GAP) at the cytoplasmic region, ultimately modulating cellular adhesion behaviour. However, the structural mechanism underlying the receptor activation remains largely unknown. Here we report the crystal structures of the semaphorin 6A (Sema6A) receptor-binding fragment and the plexin A2 (PlxnA2) ligand-binding fragment in both their pre-signalling (that is, before binding) and signalling (after complex formation) states. Before binding, the Sema6A ectodomain was in the expected 'face-to-face' homodimer arrangement, similar to that adopted by Sema3A and Sema4D, whereas PlxnA2 was in an unexpected 'head-on' homodimer arrangement. In contrast, the structure of the Sema6A-PlxnA2 signalling complex revealed a 2:2 heterotetramer in which the two PlxnA2 monomers dissociated from one another and docked onto the top face of the Sema6A homodimer using the same interface as the head-on homodimer, indicating that plexins undergo 'partner exchange'. Cell-based activity measurements using mutant ligands/receptors confirmed that the Sema6A face-to-face dimer arrangement is physiologically relevant and is maintained throughout signalling events. Thus, homodimer-to-heterodimer transitions of cell-surface plexin that result in a specific orientation of its molecular axis relative to the membrane may constitute the structural mechanism by which the ligand-binding 'signal' is transmitted to the cytoplasmic region, inducing GAP domain rearrangements and activation.     

Regulation of Ca2+-dependent K+-channel activity in tracheal myocytes by phosphorylation

Isoprenaline is a beta-adrenergic agonist of clinical importance as a remedy for asthma. In airway smooth muscle its relaxant action is accompanied by hyperpolarization of the membrane and elevation of the level of intracellular cyclic AMP. Hyperpolarization and relaxation are also induced by drugs such as forskolin, theophylline and dibutyryl cAMP, indicating that cAMP-dependent phosphorylation is involved in producing the electrical response. Cyclic AMP-dependent protein kinase (protein kinase A) has been reported to activate Ca2+-dependent K+ channels in cultured aortic smooth muscle cells and snail neurons. The membrane of tracheal smooth-muscle cells is characterized by a dense distribution of Ca2+-dependent K+-channels. We have now examined the effect of isoprenaline and protein kinase A on Ca2+-dependent K+-channels in isolated smooth muscle cells of rabbit trachea, using the patch-clamp technique. Our results show that the open-state probability of Ca2+-dependent K+-channel of tracheal myocytes is reversibly increased by either extracellular application of isoprenaline or intracellar application of protein kinase A. We also show that this effect is significantly enhanced and prolonged in the presence of a potent protein phosphatase inhibitor, okadaic acid.     

Vitamin A and tumor immunity

Summary Intraperitoneal administration of vitamin A into the BALB/c mice inoculated with a syngeneic fibrosarcoma, Meth A, caused a remarkable augmentation of tumor rejection. A cell-depletion technique revealed that the primary effector cells responsible for the augmented rejection were Thy-1 positive, Lyt-1 negative, Lyt-2 positive lymphocytes, suggesting the involvement of cytotoxic lymphocytes.This work was supported in part by a Grant-in-Aid for scientific research from the Ministry of Education, Science and Culture, Japan, and in part by a Grant-in-Aid for cancer research from the Fukuoka Cancer Society, Japan.We thank Mr M. Fujiki and Miss A. Maeda for excellent technical assistance.     

The physiology of the smooth muscle: an interdisciplinary review—part II

Summary In the guinea pig taenia coli, when glycogen is depleted by repeating Ca-induced contracture in excess K solution containing no glucose, the tension cannot be maintained. The decrease in tension is accompanied by reduction of high energy phosphate compounds and oxygen consumption. When substrate is readmitted to the glycogendepleted preparation in the presence of 2.4 mM Ca and 20 mM K, the first response is hyperpolarization of the membrane and relaxation, and this is followed by depolarization and development of contracture. The latter response is blocked by verapamil, suggesting that energy supply increases the Ca conductance of the plasma membrane. The early response is considered to be due to activation of electrogenic Ca pump, since this is not affected by ouabain as well as removal of Na and K. ATP produced by substrate readmission is probably preferentially utilized for Ca pump activation to reduce the intracellular. Ca. The recovery of tension is likely to be brought about by ATP supply not only to the contractile machinery but also to the plasma membrane to remove inactivation of Ca conductance. It is postulated that as the energy source is depleted, energy consumption is automatically limited by suppressing Ca influx, as a selfdefence mechanism. Since HB is as effective as glucose in the recovery of these processes, and also in the activation of electrogenic Na pump, the matabolic pathway of oxidative phosphorylation alone can support these functions without a contribution of the glycolytic pathway.     

Molecular evidence on evolutionary switching from particle-feeding to sophisticated carnivory in the calanoid copepod family Heterorhabdidae: drastic and rapid changes in functions of homologues

The oceanic calanoid copepod family Heterorhabdidae is unique in that it comprises both particle-feeding and carnivorous genera with some intermediate taxa. Both morphological and molecular (nuclear 18S and 28S rRNA) phylogenetic analyses of the family suggest that an evolutionary switch in feeding strategy, from transitions of typical particle-feeding through some intermediate modes to sophisticated carnivory, might have occurred with the development of a specially designed ‘poison’ injection system. In view of the small amount of genetic differentiation among genera in this family, the switching of feeding modes and re-colonization from deep to shallow waters might have occurred over a short geological period since the Middle to Late Miocene.     

Photonics: lasers producing tailored beams

Compact lasers that can produce a range of beam patterns are important for progress in several areas, including the improvement of optical tweezers, ultra-high-density optical memory and microfluidics. Here we engineer photonic crystals to generate semiconductor lasers that produce a range of beam patterns while maintaining stable single-mode oscillation. Our results could contribute to the realization of compact lasers that are capable of producing diverse beam patterns on demand.