The properties of cytochrome f and P700 in chloroplasts suspended in fluid media at sub-zero temperatures.

1. The properties of P700 and cytochrome f have been studied at sub-zero temperatures in chloroplasts suspended in a medium containing 50% (v/v) ethylene glycol. The dark reduction of these components after a period of illumination provided information about the rate-limiting step of photosynthetic electron transport under these conditions. 2. The oxidation of P700 on illumination in the presence of methyl viologen and its subsequent dark reduction can be observed at -35 degrees C. This cycle of reactions could be repeated many times. The rate of reduction was increased by NH4Cl and reduction was inhibited by 3(3,4-dichlorophenyl)-1,1-dimethylurea. 3. The oxidation and reduction of cytochrome f could also be observed under similar conditions. The activation energies for the reduction of cytochrome f and P700 are similar (about 75 kJ mol-1) and the reduction of cytochrome f is also inhibited by dichlorophenyldimethylurea and stimulated by NH4Cl. 4. The reduction of both cytochrome f and P700 seemed to follow first-order kinetics, but the t1/2 for the redcution of the cytochrome was at least three times that for the reduction of P700 at the same temperature. It was concluded that the results were only compatible with a model in which the main pathway of electrons from plastoquinone to P700 involved cytochrome f if the equilibrium constant between the cytochrome and P700 was very much less than that expected from their redox potentials.     

Isolation and Identification of a Genus, Chromobacterium, Not Previously Found on Processed Poultry

An organism identified as Chromobacterium lividum was isolated from processed poultry in Georgia.     

Absence of metabolic cooperation in PHA-stimulated human lymphocyte cultures

Intercellular communication as detected by ionic coupling and gap junction formation has been reported previously in phytohemagglutinin (PHA)-stimulated lymphocyte cultures. PHA-stimulated mixtures of normal and hypoxanthine phosphoribosyl-transferase (HPRT) deficient lymphocytes did not exhibit metabolic cooperation when incubated with [³H]hypoxanthine. These observations suggest that there may be selectivity for compounds transferred by lymphocyte junctions during intercellular communication.     

A peptide-like substance from pituitary that acts like morphine. I. Isolation.

A method is described for extraction from bovine pituitary glands of a substance that shows several properties characteristic of opiates. The material inhibits the twitch tension of the electrically stimulated guinea pig longitudinal muscle-myenteric plexus preparation and of the electrically stimulated mouse vas deferens. This inhibition is reversed and blocked by the opiate antagonist naloxone. The extract also inhibits binding of the opiate agonist etorphine and the opiate antagonist naloxone to stereospecific binding sites in synaptic membranes of guinea pig brain. The inhibition of naloxone binding is decreased by Na⁺ in the manner characteristic of opiate agonists. The physiologic role of the pituitary opioid remains to be investigated.     

A peptide-like substance from pituitary that acts like morphine. 2. Purification and properties.

We have demonstrated the existence of a peptide-like opioid in bovine and porcine pituitary, and determined some of its properties. It is an opioid agonist on the guinea pig myenteric plexus-longitudinal muscle preparation, and on the mouse vas deferens, and it binds to opiate receptors in homogenates of guinea pig brain. Its physiologic role and its possible presence in hypothalamic or other brain regions remain to be determined.     

The induction by X-rays of chromosome aberrations in male guinea-pigs, golden hamsters and rabbits. II. Properties of translocations induced in post-meiotic stages.

Translocations induced by X-rays in post-meiotic germ cells of male guinea-pigs, golden hamsters and rabbits were studied cytologically in the F1 sons of the irradiated males. The percentage of spermatocytes displaying multivalent configurations varied with the translocation, but the average percentage appeared to depend on the species: fewer quadrivalents were observed in hamster than in guinea-pig heterozygotes and most were recorded for rabbit heterozygotes. Chain quadrivalents were more abundant than ring quadrivalents at meiosis for the guinea-pig and hamster, in contrast to the mouse. Too few translocation heterozygotes were examined to determine which meiotic configuration was the more prevalent in the rabbit. In all three species, as in the mouse, translocations were found which caused male sterility, due to partial or complete failure of spermatogenesis, although most translocations caused semi-sterility. For these semi-sterile males both the frequency and time of embryonic death in the progeny appeared to be the same as in the mouse. It is concluded that similar types of chromosome aberrations are induced by X-rays in post-meiotic germ cells of male guinea-pigs, rabbits, golden hamsters and mice.     

RNA POLYMERASE ACTIVITY IN VARIOUS CLASSES OF NUCLEI FROM DIFFERENT REGIONS OF RAT BRAIN DURING POSTNATAL DEVELOPMENT

—The changes in the wet weight and the numbers of cell nuclei recovered from the cerebral hemispheres, the cerebellum and the brain stem of rats from the period of 5–30 days after birth have been determined. In parallel a study has been made of the RNA polymerase activity, both in the unfractionated nuclei from these regions and in the nuclei separated by zonal centrifugation. In general there is a considerable decline in activity during this period, which occurs in all class of nuclei although not to the same extent. The most dense nuclei from the cerebellum retain relatively high activity at 20 days after birth, possibly due to the contribution of the microneuronal nuclei.     

Factors affecting trimethylarsine and dimethylselenide formation by<Emphasis Type="Italic">Candida humicola</Emphasis>

Selenite, selenate, and tellurate inhibited the conversion of arsenate to trimethylarsine byCandida humicola. Trimethylarsine disappeared from the gas phase when incubated withC. humicola in the presence of selenium or tellurium salts. The fungus generated dimethyl-selenide from selenite and selenate and an unidentified gas from tellurate. Sulfate but not arsenate, tellurate, or phosphate inhibited the conversion of selenate to dimethylselenide. Arsenate-grown cells generated trimethylarsine from arsenate, and selenate-grown cells formed dimethylselenide from selenate with almost no lag phase. Cells grown in media with selenate or with no additions only formed the alkylarsine from arsenate after a lag phase, and those grown in solutions with arsenate or no additions produced dimethylselenide slowly from selenate.     

The autotrophic growth of Micrococcus denitrificans on Methanol.

Ribulose bisphosphate carboxylase is present at a high specific activity in extracts of methanol-grown Microccus denitrificans. Enzymic and physiological evidence indicates that, during growth on methanol, the ribulose bisphosphate cycle is the route of carbon assimilation.     

Differentiation in Coprinus lagopus

Fruit-body expansion was studied in Coprinus lagopus (sensu Buller) following surgical procedures. Elongation occurred after denuding mushroom caps of essentially all peripheral scales. Young primordia (1–5 mm) failed to develop after vertical bisection. Older primordia (e. g. 10 mm) expanded 3–4-fold after vertical bisection or quadrisection, underwent autolysis and basidiospore production. An amorphous brown gel in the stipe lumen disappeared during development of bisected primordia. Stipes isolated from primordia expanded autonomously and exhibited negative geotropism when incubated upside down or when the stipe apex was removed. Displacement of charcoal particles dusted on intact stipes revealed the most active zone of expansion to be the upper mid-region of the stipe. Segmented stipes likewise showed most active elongation in the mid-region. Vertically bisected stipes also expanded.