Evidence for two conformers of the beta subunit of tryptophan synthase in solution.

To explain our finding that the dimeric beta subunit of tryptophan synthase is only 50% inactivated by beta-chloro-L-alanine (Ahmed, S. A., Ruvinov, S. B., Kayastha, A. M., and Miles, E. W. (1991) J. Biol. Chem. 266, 21548-21557), we have extended our investigation using spectroscopic, steady-state kinetic, and electrophoretic methods. The spectroscopic properties of the half-active beta 2 dimer and the reactivation after alkali treatment show that the inactivation proceeds by an "enamine" mechanism. Although the fully active beta 2 dimer associates with the tryptophan synthase alpha subunit to form alpha 2 beta 2 complex, the inactive beta subunits in the half-active enzyme associate weakly or not at all with the alpha subunit. Our results provide evidence for two conformers of the beta subunit in solution: one is rapidly inactivated by beta-chloro-L-alanine and the other is not inactivated. Thermal inactivation studies and non-denaturing polyacrylamide gel electrophoresis of the half-active enzyme show that the beta 2 dimer exists in both homologous and heterologous combinations of these two forms. After removal of the reaction products and unreacted beta-chloro-L-alanine from the half-active beta 2 dimer by gel filtration, further incubation with beta-chloro-L-alanine results in the loss of 50% of the remaining activity. This result suggests that the subunits undergo rearrangement via an intermediate monomer form to regenerate the two conformers of the active beta subunit. This mechanism of rearrangement is supported by our finding that the extent of inactivation increases at lower concentrations of the beta 2 dimer.     

Effect of cyclic AMP on fructose utilization, progressive motility and protein synthesis by ram spermatozoa

Ejaculated washed ram spermatozoa showed consistent increases in the intracellular concentration of cyclic 3', 5'-adenosine monophosphate (cAMP) after incubation for 15 minutes with the phosphodiesterase (PDE)-inhibitors, theophylline and caffeine. In vitro addition of cAMP or PDE-inhibitors to ram semen also stimulated and maintained sperm motility and enhanced the rate of fructose utilization. The same doses of cAMP or theophylline significantly stimulated the rate of protein synthesis by the washed spermatozoa, while the PDE-stimulator, imidazole, inhibited protein synthesis significantly. The stimulatory effect of cAMP on sperm protein synthesis was not affected by cycloheximide, but was abolished by the mitochondrial inhibitor, chloramphenicol. The present results indicate a positive correlation between the intracellular concentration of cAMP and the rates of progressive motility, fructose utilization, and protein synthesis by ram spermatozoa. The results suggest that the effect of cAMP is associated with the synthesis of mitochndrial proteins which may be involved with the observed enhancement of sperm motility and metabolism. The data also indicate that cAMP map act either as a first or a second messenger in mature spermatoza.     

Group composition in wild and commensal hamadryas baboons: A comparative study in Saudi Arabia

Papio hamadryas was surveyed throughout its range in Saudi Arabia and was observed at altitudes ranging from 0 to 2300 m. Wild populations occur along the whole range of altitude, while commensal populations are only found above 850 m altitude. No variation in group size was found with altitude. Comparison of wild and commensal populations showed the following. (1) Their composition in terms of age and sex classes, overall adult sex ratios, and group size does not significantly differ. (2) Groups of both populations include, in similar proportions, three types of parties: one-male units (>70%), two-male units (>13%), and a few other units of variable composition. (3) The mean size of commensal parties is significantly larger than in the wild population; specifically one-male units are larger in the commensal population due to a larger number of females per male. Thus, female distribution in commensal groups is more inequitable than that in wild groups. (4) Finally, the number of females included in two-male units increases with altitude. These differences are discussed in terms of food availability and predator pressure and are compared with results obtained on other Arabian and Ethiopian populations.     

The distribution ofPapio hamadryas in Saudi Arabia: Ecological correlates and human influence

We describe the distribution ofPapio hamadryas in Saudi Arabia in relation to ecological constraints and recent changes in human activities and land use. Baboons are present only in the Sarawat and southern Hijaz mountains, which border the Red Sea in the southwestern region of the country. Our distribution data confirms that their range, described as of 1981, should be extended 200 km northward, from 21°40N (Taif) to 23°20N (Al Akhal). This new limit of range is not due to recent deployment of the baboons, but instead corrects inaccurate surveys by previous reporters. Ecological factors that affect baboon distribution include low annual rainfall (less than 100 mm per yr), which limits baboon range in the north and east, and the absence of suitable sleeping cliffs in the coastal plain, which limits their range in the west. Relative abundance is discussed in relation to vegetation and predator distribution. Human influence is also significant: commensal troops persist near urban centers, while agricultural development reduces baboon numbers in some regions. Habitat characteristics are discussed in comparison with similar data on the range of hamadryas in Ethiopia.     

Studies on the mechanism of haloacetonitrile-induced gastrointestinal toxicity: interaction of dibromoacetonitrile with glutathione and glutathione-S-transferase in rats

The haloacetonitrile, dibromoacetonitrile (DBAN), is a direct-acting genotoxic agent that has been detected in drinking water. In a time course study, male Sprague-Dawley rats were treated with DBAN (75 mg/kg PO), and killed at 0.5, 1, 2, and 4 hr after treatment. In a dose response study, animals were treated orally with various doses of DBAN (25, 50, 75, and 100 mg/kg) and killed at one-half hour after treatment. Control animals received 1 ml/kg PO of the vehicle dimethyl sulfoxide (DMSO). In both experiments blood and organs were collected and stored at -80 degrees C until the time of analysis. At 0.5 hr after treatment, a single oral dose of DBAN caused a significant decrease of glutathione (GSH) concentrations in liver (54% of control) and stomach (6% of control). Hepatic GSH depletion was maximal at 0.5 hr and rebound to the control levels by 4 hr. In contrast, gastric GSH concentrations remained low at all time points. DBAN caused an insignificant change in both kidney and blood GSH levels. DBAN significantly inhibited glutathione-S-transferase (GST) activity in liver and stomach. Hepatic GST inhibition was maximal (34% of control) at 2 hr and minimal (80% of control) at 4 hr. Meanwhile, in the stomach GST activity was inhibited at 1 hr (60% of control) and remained low at all times after treatment. Both GSH depletion and GST inhibition were dose-dependent. This study indicates that GSH and GST play an important role in the metabolism and detoxification of DBAN in rats. The prolonged depletion of GSH and inhibition of GST in the gastrointestinal (GI) tissues suggest that the GI tract is a major target for DBAN toxicity.     

Naltrexone partially inhibits the estrogen-induced increase in prolactin secretion and anterior pituitary weight

The effects of naltrexone, a specific opiate antagonist, on stimulation by estradiol benzoate (EB) of prolactin (PRL) release and anterior pituitary (AP) weight, were studied in gonadectomized female and male Sprague-Dawley rats. One week after castration, rats were injected for 10 days once daily with 2 μg EB alone, or together with twice daily injections of 2 mg naltrexone/kg body weight (BW). Blood was collected for radioimmunoassay of PRL by orbital sinus puncture on days 0 and 6, and by decapitation on day 11, at which time the AP was quickly removed, weighed and assayed for PRL.Serum PRL concentrations and AP weights were significantly increased by EB administration. These effects of EB were partially but significantly inhibited by naltrexone. These results suggest that endegenous opiates may be involved in the estrogen-induced rise in serum PRL and increase in pituatary weight.     

Effect of soil moisture stress on yield,nodulation and nitrogenase activity ofMacroptilium atropurpureum cv. Siratro andDesmodium intortum cv. Greenleaf

Summary The effect of soil moisture stress on growth, nodulation and nitrogenase activity of two tropical forage legumes,Macroptilium atropurpureum cv. Siratro andDesmodium intortum cv. Greenleaf was studied in a pot experiment. After ten weeks growth, the highest moisture stress (20 per cent water holding capacity) significantly reduced only the top weight of both plants. Moisture stress progressively retarded top growth in the two legumes. Similar trends were also observed in defoliated plants. Moisture stress had little or no effect on the nodulation or nitrogenase activity of the plants.     

Eocyzicus spinifer sp. nov. (Conchostraca: Cyzicidae) from Iraq

A new Conchostracan species, Eocyzicus spinifer from Iraq is described. A table is given to distinguish the known species of the genus Eocyzicus.