The effect of glucose on the expression of extracellular protein genes by Staphylococcus aureus strain V8

The bacteria from overnight cultures (20 h) of S. aureus V8 and exp negative mutant K6812-1, grown, aerobically, in 3% (w/v) Tryptone Soya Broth, at 37 degrees C, were resuspended in fresh medium, in the case of the parent strain +/- 1% (w/v) glucose, without change in bacterial density. During a 6 h incubation period there was an approximate doubling of bacterial density, to the same level, in each case. However, exoprotein production by the mutant was only 20% that of the parent whilst the addition of glucose to the V8 strain resulted in a tenfold reduction in the exoprotein formed. SDS-polyacrylamide gel electrophoresis showed that the exoprotein patterns of both organisms after 6 h incubation were the same as those observed in the overnight cultures whilst the presence of 1% (w/v) extra glucose changed the pattern produced by the parent to one similar to that of the mutant. The results showed that conditions which lead to the rapid formation of glucose catabolites produced an effect consistent with the inhibition of the activity of the exp gene product.     

Proteinase-activated receptor 4 (PAR4): action of PAR4-activating peptides in vascular and gastric tissue and lack of cross-reactivity with PAR1 and PAR2.

We studied the actions of the human and murine proteinase-activated receptor 4 (PAR4) derived receptor-activating peptides (APs), GYPGQV-NH2 (GQV-NH2) and GYPGKF-NH2 (GKF-NH2), (i) to activate-desensitize either PAR1 or PAR2 in cultured cell systems (calcium signalling in PAR1/PAR2-bearing human HEK cells and in rat KNRK cells expressing either rat or human PAR2) and (ii) to affect contractility in rat aorta (RA) and rat gastric longitudinal muscle (LM) preparations in vitro. We found that neither PAR1 nor PAR2 was affected by concentrations of the PAR4-APs (800 microM) that caused both an endothelium-dependent nitric oxide mediated relaxation of preconstricted RA tissue and a contractile response in the LM preparation. The potencies (EC50 values 300 to 400 microM) of GQV-NH2 and GKF-NH2 for causing a relaxant effect were identical and comparable with the potency of GQV-NH2 for causing a contractile effect in the LM. However, the potencies of the PAR4-APs in the RA and LM preparations were 20- to 150-fold lower than the potency of the receptor-selective PAR1-AP, TFLLR-NH2. We conclude that the PAR4-APs do not activate either PAR1 or PAR2, and we suggest that along with PAR1 and PAR2, PAR4 may also be present in rat vascular and gastric smooth muscle.     

Germination, respiration, and adenylate energy charge of seeds at various oxygen partial pressures

The effect of O₂ partial pressure on the germination and the respiration of 12 cultivated species was studied. The reciprocal of the time necessary to observe rootlet emergence in 50% of the seeds was used to approach the germination rate. The maximum germination and respiration rates were reached in most seeds at O₂ pressures close to that of air. Decreasing the O₂ pressure produced a gradual decrease of the germination rate. The seeds could be classed in two groups according to their response to low O₂ pressures. Group I includes lettuce, sunflower, radish, turnip, cabbage, flax, and soybean: at O₂ pressures close to 2 kilopascals, the germination in this group was stopped and the adenylate energy charge was lower than 0.6. Group II includes rice, wheat, maize, sorghum, and pea. The germination rate of these seeds was also gradually decreased by lowering the O₂ partial pressure but germination still occured, very slowly, at 0.1 kilopascal; the adenylate energy charge remained higher than 0.6. These differences in the germination rates and adenylate energy charge values could not be explained by differences in the sensitivity of respiration to O₂.     

Changes in R–R variability before and after endurance training measured by power spectral analysis and by the effect of isometric muscle contraction

 The long-term conditioning effects of physical training on cardiorespiratory interaction in 11 young healthy males were studied. Significant increases in maximum oxygen uptake (V˙O_2max)(P<0.05) and decreases in heart rate (P<0.05) were achieved in all subjects following a 6-week training programme consisting of cycling for 25min each day at a work level that increased heart rate to 85% of maximum. Heart rate variability, measured as the differences between the maximum and minimum R–R interval in a respiratory cycle, increased in nine of the subjects and decreased in two. The respiratory-cycle-related high-frequency peak in the power spectral plot of R–R variability also showed significant increases in the same nine subjects and decreases in two. The latter result was similar after normalisation of the data for changes in heart rate by calculating the common coefficient of variance (CCV=HFR–R×<∮∮), where HF is the high-frequency component of the power spectral plots, using a further measure of vagal tone it was shown that, for all subjects, the R–R interval change in response to isometric contractions of the arm flexors in one respiratory cycle were significantly greater after training. These data suggest that cardiac vagal tone is increased by aerobic training for all subjects and that this is accompanied by a respiratory sinus arrhythmia (RSA) in most, but may be associated with a decrease in RSA in subjects with a very low (< 50 beats⋅min^-1 heart rate. Accepted: 23 April 1996     

Metabolizable energy requirements for maintenance and growth of Awassi lambs

Twenty four Awassi lambs (mean BW 24.4 kg) were used in a two periods experiment to measure maintenance (zero growth) and growth requirements of metabolizable energy (ME). During the pre-treatment period (period 1, 3 weeks) all lambs were maintained at a constant level of feed intake (2% BW). During the treatment period (period 2, 10 weeks) the lambs were divided into four equal groups and fed different amounts (2, 3, 4 and 5% of BW). Six additional lambs of similar BW and age were killed at the beginning of the experiment to compare final empty body weight (FEBW) with initial body weight (IBW). Twelve lambs, divided into four equal groups were fed the experimental diet in the same amounts as in the growth experiment (period 2) to determine the digestibility of energy.

Energy requirement for maintenance (EM) was measured by both constant weight technique, using data collected during period 1, and regression technique by regressing ME intake on body weight gain (BWG) and empty body weight gain (EBWG). EM measured during the constant weight period (pre-treatment) and overall experimental period (pre-treatment plus treatment periods) were 0.482 and 0.466 MJ of ME per kg M^0.75 per day. Predicted energy requirements for growth (Eg) calculated from equations derived during the treatment period were 0.433, 0.623, 0.782, 0.910 and 1.007 (MJ per kg M^0.75 per day) for the growth rates 50, 100, 150, 200, and 250 (g per day) respectively. It is concluded to be more appropriate to use the values derived during the overall experimental period for maintenance and the overall treatment period for growth as they are most applicable to production situations.     

Isoflavone biosynthesis in Onobrychis viciifolia: Formononetin and texasin as precursors of afrormosin

4,2′,4′-Trihydroxychalcone- [carbonyl-¹⁴C], formononetin- [Me-¹⁴C] and texasin- [Me-¹⁴C] were all good precursors of afrormosin (7-hydroxy-6,4′-dimethoxyisoflavone) in Onobrychis viciifolia seedlings, and a biosynthetic pathway involving these intermediates is proposed. 2′,4′-Dihydroxy-4-methoxychalcone- [carbonyl-¹⁴C] and daidzein-[carbonyl-¹⁴C] were poor precursors. Incorporations into formononetin were also recorded.