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Biomedical subjects

A M Rojas

Publications and source records attributed to A M Rojas.

29 records · Page 2Linked to original sources
PubMed1991

How does ppGpp affect translational accuracy in the stringent response?

With an in vitro poly(Phe) synthesis system we have tested recent models concerning translational accuracy in the stringent response during aminoacid starvation. We have found that cognate, deacylated tRNA of very high concentrations is unable to block the A-site. No influence of EF-Tu.ppGpp on ribosomal proofreading has been found. Alternative mechanisms to keep translational errors low by the stringent response are discussed.

Amino Acids↗
PubMed1990

How many EF-Tu molecules participate in aminoacyl-tRNA binding and peptide bond formation in Escherichia coli translation?

We have observed that two EF-Tu.GTP cycles are required to make one peptide bond during steady-state translation in an accurate and fast poly(U) translation system prepared from Escherichia coli. We have also found that there are two complexes of EF-Tu.GTP bound to one molecule of aminoacyl-tRNA under our experimental conditions. We suggest, on the basis of these data, that aminoacyl-tRNA enters the ribosomal A-site in a pentameric complex together with two EF-Tu and two GTP molecules. When the tRNA is delivered to the ribosome two GTP molecules are hydrolyzed. It is possible that the functional role of such an EF-Tu dimer is related to the function of the two L7/L12 dimers in the large ribosomal subunit.

Escherichia coli↗
PubMed1986

Dendritic development in the neocortex of adult rats following a maintained prenatal and/or early postnatal life undernutrition.

The Golgi-Cox method was used to study the maturation of the large pyramidal cells of the Vth cortical layer in three groups of adult rats: one subjected to undernutrition during the first month of life, another throughout the first 2 mth of life, and the last one during gestation and the suckling period. The main alterations consist of a decrease in the number and span of dendritic basilar processes of large pyramidal cells. In animals malnourished during prenatal life and the suckling period the reduction of the basal dendritic arborization was more apparent. It is postulated that the vulnerable period for the basal dendritic development occupies the period from the end of pregnancy until the first 3 wk of postnatal life in the rat (suckling period). Noxious influences acting during this phase induce sequelae that cannot be reversed by subsequent refeeding. A maintained nutritional insult during prenatal and early postnatal life induces the most severe changes in dendritic arborizations, compared to those resulting from a prolonged postnatal malnutrition.

Animals↗
PubMed1985

Effect of theophylline on nuclear retention of oestrogenreceptor complexes: correlation with oestrogen responses.

In the ovariectomized adult rat uterine oedema induced by 0.01 and 0.1 micrograms oestradiol-17 beta/100g body weight increased further in the presence of theophylline. Nuclear retention of oestrogen-receptor complexes also increased in response to theophylline both in vivo and in vitro. Theophylline decreased the number of eosinophils in the blood and concurrently decreased oestrogen-induced uterine eosinophilia at doses of 0.001, 0.01, 0.1, 1, 10 or 30 micrograms oestradiol/100 g body weight, through a mechanism independent of glucocorticoids. There was, therefore, no correlation between changes in the number of uterine eosinophils and changes in uterine wet weight induced by theophylline and oestrogen. It is suggested that the presence of oestrogen-receptor complexes in the nucleus for at least 4 h is a prerequisite for the induction of uterine oedema and growth in the presence of theophylline and oestradiol-17 beta.

Animals↗
PubMed1984

ppGpp inhibition of elongation factors Tu, G and Ts during polypeptide synthesis.

The inhibition of elongation factors G, Tu and Ts by ppGpp was studied in vitro in a translation system with missense frequency and elongation rate similar to those in vivo. ppGpp inhibits EF-G with KI = 6 X 10(-5) M. When ppGpp is in twofold excess over GTP and EF-G is the rate-limiting component, the elongation rate is reduced twofold by ppGpp. EF-Tu is inhibited with KI = 7 X 10(-7) M in the absence of EF-Ts. When EF-Ts is added, the binding of ppGpp to EF-Tu becomes successively weaker. 1/KI depends linearly on 1/[Ts] and the intercept at the abscissa gives KI = 4 X 10(-5) M. This reflects the binding of ppGpp to the binary TuTs complex. The slope reveals that the binding of EF-Ts to the TuMS binary complex is strong (10(-6) M). ppGpp may thus inhibit the cycling of EF-Tu indirectly by the removal of the free EF-Ts by its adsorption to TuMS, as well as directly by simple binding to Tu. EF-Tu inhibition by ppGpp can be fully reversed by high levels of aminoacyl-tRNA only in the presence of EF-Ts and at low ribosomal activity. Our in vitro observations have been extrapolated to in vivo conditions with conclusions as follows: Under strong amino acid starvation ppGpp in twofold excess over GTP cannot reduce significantly the elongation rate of ribosomes and thereby restore the errors to their normal levels as in the stringent response. Under weak starvation, in contrast, a significant rate reduction can be achieved by the trapping of EF-Ts in complex with TuppGpp.

Bacterial Proteins↗
PubMed1983

Multiple mechanisms of regulation of estrogen action in the rat uterus: effects of insulin.

Eosinophils appear in the rat uterus in the presence of estrogen. The level of these cells in the uterus depends on the number of blood eosinophils. Insulin is an eosinopenic hormone in the blood and, therefore, could regulate estrogenic responses mediated by these cells in the uterus. Estrogen-induced uterine edema and eosinophilia at doses of 0.01,. 0.1, 1, 10, and 30 micrograms 17 beta-estradiol (E2)/100 g BW are inhibited by insulin. Estrogen binding by uterine eosinophils in vitro decreases in the presence of insulin, suggesting another explanation for the observations in the uterus in vivo. Injection of insulin alone or in combination with 0.01, 0.01, 0.1, or 1 microgram E2/100 g BW increases uterine RNA and protein contents by 6 h. Inactive insulin does not modify any of these stimulatory effects of estrogen. The results support the idea of two separate receptor systems for estrogens in the rat uterus: the eosinophil receptor system, which mediates estrogen-induced uterine edema, and the cytosol-nuclear receptor system, which mediates estrogen-induced uterine RNA and protein syntheses.

Animals↗
PubMed1982

Theophylline-estrogen interaction in the rat uterus: role of the ovary.

Uterine edema induced by 0.1 microgram/100 g body wt of estradiol further increases in the presence of theophylline. Theophylline alone or in the presence of 0.001, 0.01, 0.1, and 1 microgram/100 g body wt of estradiol increases uterine RNA and protein content 6 h after its administration, as compared with the same doses of estradiol alone. Both phenomena disappear in the ovariectomized immature rat, suggesting that theophylline potentiates the action of gonadotropins, increasing the synthesis of endogenous ovarian estrogens by the immature ovary. Theophylline decreases the number of eosinophils in the blood and concurrently decreases estrogen-induced uterine eosinophilia at doses of 0.01, 0.1, 1, 10, and 30 micrograms/100 g body wt of estradiol. Estrogen binding by uterine eosinophils in vitro increases in the presence of theophylline. This effect of theophylline could also explain the increase in vivo in estrogen-induced uterine edema.

Animals↗
PubMed1982

Effects of thyroid hormone on some uterine responses to estrogen.

Uterine edema induced by 0.1 microgram 17 beta-estradiol (E2)/100 g BW, as well as uterine eosinophilia induced by 0.01, 0.1, 1, 10, and 30 micrograms E2/100 g BW, decrease in the presence of 20 micrograms T3 or T4/100 g BW in the immature rat. Estrogen binding by uterine eosinophils and the number of eosinophils in the blood also decrease with T3 or T4, suggesting an explanation for the findings in the uterus. Thyroid hormones alone or in the presence of 0.001, 0.01, 0.1 and 1 microgram E2/100 g BW, increase the uterine RNA content 7 h after administration compared with the same doses of E2 alone. This response is not associated with any further increase in the urine protein content. The results show a dissociation between the effects of estrogen on RNA or protein levels, which are decreased by thyroid hormones, and some early estrogenic responses (uterine edema and eosinophilia), which are decreased by thyroid hormones.

Animals↗
PubMed1982

Effect of insulin and epinephrine on some early oestrogenic responses in the rat uterus.

Oestradiol induces uterine eosinophilia and oedema, both in the intact immature rat and in the adult ovariectomized rat. These responses are decreased in ovariectomized-adrenalectomized adult rats, in adrenalectomized immature rats and in medullectomized immature rats. Pre-treatment with L-epinephrine restored both oestrogenic effects. Insulin inhibits oestrogen binding by uterine eosinophils and concurrently decreases oestrogen-induced uterine oedema and eosinophilia. These phenomena do not occur with inactive insulin. Insulin also induces blood eosinopaenia, suggesting an explanation for the findings in the uterus.

Adrenalectomy↗
PubMed1979

Interaction between theophylline and oestrogen in the rat uterus.

Theophylline alone or in the presence of 0.001, 0.01, 0.1 or 1 microgram oestradiol-17 beta/100 g body wt increase uterine RNA and protein content 6 h after administration. Uterine oedema induced by physiological doses of oestradiol-17 beta was increased further in the presence of theophylline. Theophylline decreased the number of eosinophils in the blood and concurrently decreased oestrogen-induced uterine oesinophilia at doses of 0.01, 0.1, 1, 10 or 30 micrograms oestradiol-17 beta/100 g body wt. Oestrogen binding by uterine eosinophils in vitro increased in the presence of theophylline. This effect of theophylline could explain the increase of oestrogen-induced uterine oedema in vivo.

Animals↗