A general pre-steady-state solution to complex kinetic mechanisms

We have developed a general method for solving transient kinetic equations using Laplace transforms. Laplace transforms can be used to transform systems of differential equations that describe pre-steady-state kinetics to systems of linear algebraic equations. The general form of the pre-steady-state solution is (formula; see text) where I(t) is the time dependence of the physically observed property of the system, n is the number of intermediates, lambda i are the observed rate constants (reciprocals of the relaxation times), t is time, and Ii are the amplitude coefficients associated with each observed rate constant. We have written a program in compiled BASIC to run on a personal computer to evaluate Ii and lambda i. The program will evaluate the rate constants and coefficients of a mechanism with eight intermediates and seven relaxation times in 4 s on an 8-MHz PC-XT equipped with a math coprocessor. The most complex mechanism that we have solved, a mechanism containing 20 intermediates and 19 relaxation times, required approximately 5 min. We believe that this method will be useful to evaluate the differences in transient properties of complex biochemical mechanisms.     

A comparison of strength and muscle endurance in strength-trained and untrained women

Muscular strength and fatigability of strength-trained (ST) and untrained (UT) women were compared during a 6-min bout of maximal rhythmic exercise involving the elbow flexor muscles given at a rate of 30 contractions.min-1. Fifteen ST and 15 UT subjects, aged 18-34 years and pair-matched for body size, were tested for differences in initial strength, final strength, absolute endurance, relative endurance, and rate of fatigue. Results revealed a significant difference in initial strength, final strength, and absolute endurance in favor of ST subjects. No significant difference was found for relative endurance, and rates of fatigue were similar for both groups. It is concluded that muscular strength and endurance are enhanced in women engaged in a training program designed primarily to increase muscular strength and hypertrophy, but fatigability is not affected.     

Mutations in Methanobacterium formicicum conferring resistance to anti-80S ribosome-targeted antibiotics

Summary Mutants of Methanobacterium formicicum resistant to the anti-80S ribosome-targeted inhibitor anisomycin were isolated and characterized. The resistance phenotype is correlated with a mutationally altered 50S ribosomal subunit. Anisomycin resistance in the mutants is accompanied by cross-resistance to other inhibitors of the 80S peptidyl-transferase centre like narciclasine, bruceantin, trichodermin and verrucarin A and by hypersensitivity to sparsomycin. This phenotype is identical to that reported for anisomycin-resistant mutants of yeast; it appears therefore, that the anisomycin interaction sites on the 70S ribosomes from M. formicicum bear the structural features typical of eukaryotic 80S organelles.     

In vitro culture of Trichogramma pretiosum on an artificial medium

The composition of an artificial medium and environmental conditions are described for the in vitro rearing of the egg parasite Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae). The medium was composed of defined amounts of protein, carbohydrates, lipid, salts, and vitamins, but also contained up to 40% insect hemolymph. The hemolymph was necessary to induce pupation. T. pretiosum eggs were obtained by dissection of Heliothis virescens (F.) (Lepidoptera: Noctuidae) eggs. In vitro reared T. pretiosum were similar in size to H. virescens reared T. pretiosum, and females were fecund.

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Résumé Les oeufs de Trichogramma pretiosum ont été obtenus par dissection d'oeufs d'Heliothis virescens. T. pretiosum Riley (Hymenoptère, Trichogrammatidae) a été élevé avec succès sur un substrat synthétique. Outre des quantités définies de protéines, glucides, lipides, éléments minéraux et vitamines, la ration contenait aussi jusqu'à 40% d'hémolymphe de Manduca sexta. L'hémolymphe était nécessaire pour induire la nymphose. En plus de la nourriture, les conditions d'environnement sont apparues extrêmement importantes pour élever T. pretiosum dans des conditions satisfaisantes. Le contrôle de l'humidité relative, en particulier, était le facteur le plus important. Les adultes produits au cours de cette étude étaient d'apparence normale; ils se sont accouplés sans problèmes, les femelles étaient fécondes et leur taille ne différait pas de celle d'individus élevés sur H. virescens.

     

ACTH 1-24-induced potentiation of norepinephrine contractile responses in aortic strips from spontaneously hypertensive (SH) and normotensive (WKY) rats

Norepinephrine (NE)-induced contractile responses were less in aortic strips from SH compared to WKY rats. ACTH 1-24 potentiated NE responses in both SH and WKY aortic strips. This effect was more potent in SH aortic strips. NE-induced contractions in SH aortic strips were less sensitive to changes in external Ca2+ levels than were those of WKY aortic strips. ACTH 1-24 did not potentiate NE responses under low external Ca2+ conditions in SH aortic strips or under high external Ca2+ conditions in WKY aortic strips. The greater sensitivity of NE responses following ACTH 1-24 in SH aortic strips may imply that this peptide is modulating a mechanism related to an impaired contractility and that Ca2+ plays a key role in the observed effects.     

Slow Orthograde Axonal Transport of Radiolabelled Protein in Sciatic Motoneurones of Rats with Short-Term Experimental Diabetes: Effects of Treatment with an Aldose Reductase Inhibitor or myo-Inositol

Abstract: This study examined the effect of streptozotocin diabetes of 5 weeks duration on the profile of slow orthogradely transported radiolabelled protein in rat sciatic motoneurones. The diabetic rats showed a retardation of the tail of the slow-component profile. This selective retardation was unaffected by treatment with an aldose reductase inhibitor, although this treatment reduced the accumulation of sorbitol and prevented the depletion of myo -inositol in the sciatic nerves of the treated diabetic rats. Other groups, treated with myo -inositol, had normal or elevated sciatic nerve myo -inositol levels in the presence of accumulated sorbitol. The axonal transport profiles from both control and diabetic myo-inositol-treated groups gave normal tail velocities but an altered shape such that retardation of the tail of the profile may have been present in both. The study concludes that rats with 5 weeks streptozotocin diabetes show retardation of the velocity of the most slowly transported proteins in sciatic motoneurones, and that this defect is not linked to the polyol pathway.