Reconstitution of a GTPase Activity a 50S Ribosomal Protein from <Emphasis Type="Italic">E. coli</Emphasis>

DURING each step of peptide chain elongation the ribosome shifts up one triplet along the messenger RNA with concomitant movement of the peptidyl-transfer RNA from the donor to the acceptor site. This process, commonly known as translocation, is triggered by a supernatant protein, factor G, which in association with the ribosome cleaves GTP into GDP and inorganic phosphate^1,2 and it has been argued that the energy liberated in this reaction is used “to carry the complex one triplet forward”³.     

Ultrastructural evidence for the biflagellate origin of the uniflagellate fungal zoospore

Summary The morphological similarities between the kinetosome and the second centriole of the zoospores of Phlyctochytrium kniepii and P. punctatum (Chytridiomycetes) suggest that the second centriole in the chytrid zoospore is a vestigial flagellum base. It is suggested that the term vestigial kinetosome may also be used when referring to the structure which is presently termed the second centriole of the chytrid zoospore. Morphological similarities between the chytrid zoospores of P. kniepii and P. punctatum and the zoospores of Rhizidiomyces apophysatus (Hyphochytridiomycetes) are noted. The possible biflagellate origin of fungi with uniflagellate zoospores is discussed. The third fiber (C fiber) of the kinetosome triplet is shown to form as an outgrowth of the B fiber of the kinetosome doublet.     

THE FINE STRUCTURE OF BLASTOCLADIELLA EMERSONII ZOOSPORES

The zoospore of Blastocladiella emersonii has been re-examined with the electron microscope. The following new findings were made. A double unit-membrane system surrounds all cell organelles except γ-bodies, vacuoles and a few fragments of membranes. Lipid granules on one side of the large mitochondrion alternate with vesicles. The kinetosome of the posterior flagellum does not have any central fibrils as previously reported; a small, cylindrical structure is found within its anterior end. An associated centriole is located next to the kinetosome. Three striated rootlets pass from the kinetosome by separate channels through the mitochondrion. There appears to be no connection between the striated rootlets and the mitochondrion. Microtubules originating at the anterior end of the kinetosome pass into the cytoplasm between the mitochondrion and the nuclear cap. Long, dense strands were observed in some nuclei. The axoneme is taken up into the spore during encystment and is found in the freshly encysted spore. No trace of the flagellar sheath has been found in the encysted spore.     

The Effects of Iron-Mediated Oxidative Stress in Isolated Renal Cortical Brush Border Membrane Vesicles at Normothermic and Hypothermic Temperatures

Experiments on renal cortical brush border membrane vesicles have been undertaken in order to assess the involvement of iron in oxidative stress at physiological temperatures and under conditions of hypothermia. A decrease in temperature stimulated iron-induced lipid peroxidation. The results are discussed in relation to the role of the oxidation state of the iron and iron(II)/iron(III) ratios in the initiation of peroxidative events.     

Effects of treadmill exercise on fuel metabolism in hepatic cirrhosis

We studied whole body and regional fuel metabolism before, during, and after 90 min of treadmill exercise at 50% of maximal aerobic capacity (VO2max) in four subjects with hepatic cirrhosis and in four normal volunteers. Rates of endogenous glucose production (EGP) were measured using D-[6-3H]glucose infusions and fuel oxidation using indirect calorimetry. In the basal state, cirrhotic subjects had similar rates of EGP compared with controls. Forearm release of alanine and lactate was significantly greater in cirrhotic subjects (P less than 0.05), suggesting increased basal rates of gluconeogenesis. During exercise, EGP increased 2- to 2.5-fold in control subjects (P less than 0.01) but did not increase in cirrhotic subjects. Despite lower glucose concentrations in cirrhotic subjects, progressive hypoglycemia did not occur during exercise, probably because cirrhotic subjects demonstrated increased plasma concentrations of fat-derived substrates and derived a greater percentage of total energy requirement from fat oxidation than did controls (P less than 0.05) and because forearm muscle glucose extraction was significantly lower in cirrhotic subjects compared with controls (0.5 vs. 3.6%, respectively; P less than 0.05). During recovery, control subjects demonstrated significant increases in EGP rates compared with both the basal and exercise periods, but cirrhotic subjects showed no increase. In conclusion, cirrhotic subjects failed to demonstrate the normal increase in EGP during and after exercise. Significant hypoglycemia during exercise did not occur, possibly because of the increased availability of fat-derived fuels, which may spare the requirement for circulating glucose as an oxidative fuel for exercising muscle tissues.     

Change in cough reflex after treatment with enalapril and ramipril.

OBJECTIVE--To find out whether enalapril or ramipril causes the sensitivity of the cough reflex to change or symptomatic cough to develop in patients with hypertension. DESIGN--Prospective, placebo controlled, double blind, randomised crossover study. SETTING--Academic units of clinical pharmacology and medicine. PATIENTS--20 Patients (nine men and 11 women) who needed to take angiotensin converting enzyme inhibitors to control hypertension. INTERVENTIONS--All patients received enalapril 10 mg daily, ramipril 10 mg daily, or placebo daily for one week in random order, with a washout period of at least one week between treatments. For assessment of sensitivity of the cough reflex the patients inhaled various concentrations of capsaicin solution in random order. MAIN OUTCOME MEASURES--Measurement of the doses of capsaicin required to cause two or more and five or more coughs or the development of a symptomatic cough. RESULTS--Blood pressure, symptoms of cough, and the sensitivity of the cough reflex to inhaled capsaicin were recorded at the start of the study and before and at the end of each treatment period. Plasma urea and creatinine concentrations and angiotensin converting enzyme activity were measured at the start of the study and the end of each treatment period. Data were analysed by two way analysis of variance. Mean blood pressure was 159/97 mm Hg at the start of the study and 152/92, 143/88, and 147/86 mm Hg after treatment with placebo, enalapril, and ramipril respectively. Mean (SE) plasma angiotensin converting enzyme activity was 2.2 (0.2) mmol/l/h after treatment with placebo and fell significantly to 1.3 (0.1) mmol/l/h and to 0.4 (0.1) mmol/l/h after treatment with enalapril and ramipril respectively. No patient complained of cough while taking placebo but three women complained of cough when taking both enalapril and ramipril. The mean (95% confidence interval) lowest dose of capsaicin causing two or more coughs was 2.4 (1.5 to 4.0), 1.8 (1.12 to 2.82), and 2.2 (1.7 to 3.0) nmol after treatment with placebo, enalapril, and ramipril respectively; none of these changes were significant. The lowest dose of capsaicin causing five or more coughs was 18.9 (13.9 to 25.8), 14.4 (8.4 to 24.5), and 15.3 (10.8 to 21.2) nmol respectively; none of these changes were significant. The three patients who complained of cough had normal sensitivity to capsaicin after treatment with placebo but had a considerably increased sensitivity after treatment with enalapril and ramipril. CONCLUSIONS--Both enalapril and ramipril increase the sensitivity of the cough reflex appreciably in patients who complain of cough during treatment, but they do not change the se     

Genetic and morphological divergence among sympatric canids

Numerous studies have suggested that the extent of character divergence observed between two sympatric species reflects the intensity of competition for resources or space. However, the influence of time on divergence is often overlooked. We examined the relationship between time and character divergence in two groups of congeneric, sympatric canids on two continents: South American foxes and African jackals. Character divergence was assessed from measurements of body mass and dental and cranial shape. Divergence time was estimated from data on mitochondrial DNA restriction site polymorphisms. Our findings indicate that African jackals are morphologically similar despite having diverged more than 2 million years ago. By contrast, South American foxes differ substantially in both size and morphology after only 250,000 years of evolution. Thus, the lack of character divergence among the African jackals cannot be explained as a result of very recent common ancestry.     

Somatostatin gene expression in the thymus gland

A complex pattern of interactions appears to exist between the immune and neuroendocrine systems. Recently, vasopressin, oxytocin and vasoactive intestinal peptide have been isolated from the thymus. Using a rat somatostatin antisense RNA probe we have demonstrated expression of the somatostatin gene in the rat thymus. Furthermore, we have shown that the levels of thymic somatostatin mRNA exhibit a bell-shaped response to dexamethasone administration. Lipocortin I and II antisense RNA probes have been used as a positive control for the effects of the dexamethasone. We would suggest that somatostatin acts in the thymus in a paracrine mode to modulate T lymphocyte development.