Transducin activation by rhodopsin without a covalent bond to the 11-cis-retinal chromophore

Rhodopsin and the visual pigments are a distinct group within the family of G-protein-linked receptors in that they have a covalently bound ligand, the 11-cis-retinal chromophore, whereas all of the other receptors bind their agonists through noncovalent interactions. The retinal chromophore in rhodopsin is bound by means of a protonated Schiff base linkage to the epsilon-amino group of Lys-296. Two rhodopsin mutants have been constructed, K296G and K296A, in which the covalent linkage to the chromophore is removed. Both mutants form a pigment with an absorption spectrum close to that of the wild type when reconstituted with the Schiff base of an n-alkylamine and 11-cis-retinal. In addition, the pigment formed from K296G and the n-propylamine Schiff base of 11-cis-retinal was found to activate transducin in a light-dependent manner, with 30 to 40% of the specific activity measured for the wild-type protein. It appears that the covalent bond is not essential for binding of the chromophore or for catalytic activation of transducin.     

Acquisition by innervated cardiac myocytes of a pertussis toxin-specific regulatory protein linked to the alpha 1-receptor

During development, the chronotropic response of rat ventricular myocardium to alpha 1-adrenergic stimulation changes from positive to negative. The alpha 1-agonist phenylephrine increases the rate of contraction of neonatal rat myocytes cultured alone but decreases the rate of contraction when the myocytes are cultured with functional sympathetic neurons. The developmental induction of the inhibitory myocardial response to alpha 1-adrenergic stimulation in intact ventricle and in cultured myocytes was shown to coincide with the functional acquisition of a substrate for pertussis toxin. A 41-kilodalton protein from myocytes cultured with sympathetic neurons and from adult rat myocardium showed, respectively, 2.2- and 16-fold increases in pertussis toxin-associated ADP-ribosylation (ADP, adenosine diphosphate) as compared to controls. In nerve-muscle cultures, inhibition of the actions of this protein by pertussis toxin-specific ADP-ribosylation reversed the mature inhibitory alpha 1-adrenergic response to an immature stimulatory pattern. The results suggest that innervation is associated with the appearance of a functional pertussis toxin substrate by which the alpha 1-adrenergic response becomes linked to a decrease in automaticity.     

Formation of virus-like particles by bone cells in mice with a high incidence of spontaneous leukemia

Bone samples from potentially leukemic and leukemic mice revealed numerous 90-to 110-nanometer particles morphologically identical to murine leukemia virus. Particles were observed budding from plasma membranes of osteocytes and osteoblasts but were most numerous in osteocyte lacunae. Particles were not observed in bone samples from mice which rarely develop leukemia.     

Anesthesia of Artemia larvae: method for quantitative study

Potency of anesthetics is quantitatively measured with laboratory-hatched larvae of the brine shrimp Artemia salina. Statistical fluctuations are minimized in that 100,000 animals are used to determine a single median anesthetic dose value. The technique was developed to study molecular mechanisms of general anesthesia.     

By Dawn's Early Light: Matutinal Mating and Sex Attractants in a Neotropical Mantid

Females of the neotropical mantis Acanthops falcata adopt a special posture at dawn which is maintained for about 20 minutes. During the same period, males fly strongly, even in the absence of females. Our studies show that in this posture females are secreting a pheromone that acts as a sex attractant. All sexual activity in this species normally occurs between dawn and sunrise. It can be triggered by any dark-to-light transition, irrespective of real time. This sexual periodicity is probably an antipredator adaptation.     

Laser altimetry of small-scale features on 433 Eros from NEAR-Shoemaker

During the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker's low-altitude flyover of asteroid 433 Eros, observations by the NEAR Laser Rangefinder (NLR) have helped to characterize small-scale surface features. On scales from meters to hundreds of meters, the surface has a fractal structure with roughness dominated by blocks, structural features, and walls of small craters. This fractal structure suggests that a single process, possibly impacts, dominates surface morphology on these scales.