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Biomedical subjects

H N Torres

Publications and source records attributed to H N Torres.

At least 73 records · Page 4Linked to original sources
PubMed1978

Kinetic studies of adenylyl cyclase of fat cell membranes. II. Comparison of activities measured in the presence of Mn++-AMP-P(NH)P and Mg++-AMP-P(NH)P. Effects of insulin, fluoride, isoproterenol, and GMP-P(NH)P.

The kinetics of fat cell adenylyl cyclase were studied, with AMP-P(NH)P and Mn++ or Mg++ as the divalent cation. In general, the reaction times were not linear. In the presence of fluoride or GMP-P(NH)P, the time curves were concave upwards; in other cases (i.e., basal activity, insulin, or isoproterenol), transient rates tended to decrease with time during the assay. Kinetic data were analyzed according to a previously described procedures (Torres et al., 1978b) which isolates two kinetic components: initial and final. With AMP-P(NH)P, kinetic activities were about ten times lower than those for ATP. With Mn++, activities were at least two-times higher than for Mg++. Spontaneous inactivation of adenylyl cyclase was higher in assays containing Mg++ than in those supplemented with Mn++. In the latter case, insulin was able to increase the inactivation rate. Fluoride and isoproterenol both activated adenylyl cyclase in both the initial and final kinetic components; under most of the conditions explored, their effects on the final component appeared to be more dramatic. Assays with GMP-P(NH)P showed inhibited activity in the initial component and increased activity in the final one. When the results obtained with AMP-P(NH)P are compared with those of ATP (Torres et al., 1978b. J. Membrane Biol. 43:000), the following differences were found: (i) in the presence of insulin and Mn++, cyclase inactivation was higher with AMP-P(NH)P than with ATP; (ii) fluoride stimulation of the final component was more marked with ATP than with AMP-P(NH)P; (iii) cyclase stimulation by isoproterenol was slightly higher with the nucleotide analog; and (iv) GMP-P(NH)P stimulation of the final component resulted in higher activity with ATP than with AMP-P(NH)P.

Adenylyl Cyclases↗
PubMed1977

Influence of cyclic 3',5'-adenosine monophosphate on uracil uptake by rifampicin treated Escherichia coli cells.

Incubation of cells from a wild type strain of E. coli with 0.3 mg/ml rifampicin for 15 minutes lead to a complete inhibition of RNA synthesis measured as the uracil incorporation into the trichloroacetic acid insoluble fraction. In these rifampicin-treated cells [14C]uracil incorporation tended to decrease during a further incubation at 37 degrees. Addition of cyclic AMP increased the inactivation of the system responsible for [14C]uracil uptake. The cyclic nucleotide effect seems to be specific since ATP or 5'AMP did not increase such inactivation.

Adenosine Monophosphate↗
PubMed1976

Regulation of uracil uptake in Escherichia coli by adenosine 3',5'-monophosphate.

Culture of a wild-type strain of Escherichia coli in the presence of cyclic AMP leads to an impairment of uracil uptake. Half maximum inhibition of uracil uptake was observed at 1.5 mM cyclic AMP. The effect seems to be specific since no inhibition was found in cultures supplemented with ATP, ADP or 5'-AMP. Similarly the inhibition was not observed in cultures of a mutant deficient in the cyclic AMP receptor protein. The inhibition in uracil uptake, found in bacteria cultured in the presence of cyclic AMP, is not a consequence of a reduction in the growth rate. On the other hand, this inhibition was observed only in cultures containing glucose or pyruvate as carbon source.

Adenosine Diphosphate↗
PubMed1976

Control of Neurospora crassa morphology by cyclic adenosine 3', 5'-monophosphate and dibutyryl cyclic adenosine 3', 5'-monophosphate.

The role of cyclic adenosine 3', 5'-monophosphate (cyclic AMP) in the control of the Neurospora asexual life cycle was studied. Endogenous cyclic AMP levels were 10 to 20 times higher in strains having the wild-type cr-1 allele than in those carrying the mutated allele. In a wild-type strain these levels remained constant throughtout the entire growth period in shaken liquid cultures, except during a short period at the beginning of the stationary growth phase. In this period a marked increase in the cyclic nucleotide level was observed. The culture of cr-1 mutant strains in the presence of cyclic AMP or its dibutyryl derivative restores some morphological properties characteristic of wild-type strains. Specifically these cyclic nucleotides stimulated the rate of mycelial elongation, as well as the differentiation of aerial hyphae.

Adenylyl Cyclases↗
PubMed1973

Effect of insulin on the growth pattern and adenylate cyclase activity of BHK fibroblasts.

BHK 21/13 fibroblasts grown in the presence of insulin show some characteristics of a transformed strain. Cells broaden, cross each other intricately, and form colonies on both polystyrene dishes and soft agar. The effect of insulin is prevented by addition of N(6)-butyryl adenosine 3':5'-cyclic monophosphate and theophylline to the culture medium. Insulin causes a decrease in the concentration of intracellular adenosine 3':5'-cyclic monophosphate and inhibition of adenylate cyclase activity in BHK fibroblast membranes. This inhibition is observed at insulin concentrations of 0.1 nM or higher.

Adenylyl Cyclase Inhibitors↗
PubMed1972

Activation of membrane-bound adenylate cyclase by glucagon in Neurospora crassa.

Membrane-bound adenylate cyclase in Neurospora crassa is activated by glucagon. Half-maximal effect is observed at hormone concentrations of about 10 nM. After solubilization of the enzyme with Lubrol-PX, the glucagon effect is lost. Incubation of neurospora cells with glucagon leads to a decrease in the activity of glycogen synthetase (EC 2.4.1.11) and to an increase in the activity of glycogen phosphorylase (EC 2.4.1.1) and in the rate of glycogenolysis.

Adenosine Triphosphate↗