Computer-assisted mathematical analysis of sigmoid biological events

A program in BASIC is described which allows accurate quantificationof some numerical parameters that can be objectively correlatedto biological indexes in sigmoid biological events. Attentionwas focused on the polymerization process of actin (a muscleprotein with a mol. wt of 42 000 daltons) studied as the variationin the OD₃₆₀ index with time. The experimental points, if plotted,can be well approximated by a rational function of the typeOD₃₆₀ = f(t), which passes through the origin and can be representedgraphically by a sigmoid curve. The program was very helpfulin comparing the experimental curves and in analysing significantparameters, such as maximum velocity and asymptote, that characterizethese curves and whose interpretation would otherwise be purelysubjective. Received on July 11, 1985; accepted on January 13, 1986     

Modulation of natural killer activity by thymosin alpha 1 and interferon

Summary A single injection of -interferon (-IFN) (30 000 units/mouse), a major biological modifier of natural killer (NK) cytolytic activity, strongly stimulated NK activity in normal mice, as expected, while the same treatment did not statistically alter the NK response in cyclophosphamide (CY)-suppressed animals.We investigated the possibility of thymosin ₁ cooperating with -IFN in boosting NK activity in CY-suppressed animals.The results show that treatment with thymosin ₁ (200 g/kg) for 4 days, followed by a single injection of -IFN 24 h before testing, strongly restored NK activity in CY-suppressed mice. Thymosin ₁ was, moreover, able to accelerate the recovery rate of NK activity in bone marrow reconstituted murine chimeras.Taken together the data support the concept that the synergic effect between thymosin ₁ and -IFN could be the result of effects on differentiation of the NK lineage at different levels.     

Action ofN-methyl-N′-nitro-N-nitrosoguanidine inRhizobium trifolii

Rhizobium trifolii was highly resistant to the lethal effect ofN-methyl-N-nitro-N-nitrosoguanidine (MNNG), but it was sensitive to the mutagenic action of this chemical. A concentration of 500g/ml yields a survival of between 1% and 10%, which allows us to obtain a higher number of mutants than lower concentrations that yield higher survival rates. Lethal damage produced by nitrosoguanidine was repaired, and repair is inhibited by acriflavine.     

Purification of Tissue Forms (Amastigotes) of Trypanosoma cruzi by Immunoaffinity Chromatography1

A rapid and simple method for the purification of amastigotes of Trypanosoma cruzi from spleens of infected mice is described. A protein A-Scpharose 4B immunoadsorbent column bound with antisera to epimastigotes of T. cruzi was used to purify the tissue forms of this parasite. Host cells and debris are not retained, and parasites can be eluted in high yields and purity. Studies of surface glycoproteins and glycolipids of the purified amastigotes with 18 lectins of various specificities revealed the presence on the parasites of receptors for N-acetylglucosamine, N-acetylgalactosamine, D-galactose, and D-mannose binding lectins.     

Mixing patterns in Amazon lakes

The diel mixing patterns of two small floodplain lakes, Lago Jacaretinga in the Amazon drainage, and Lago Cristalino in the Rio Negro system, were investigated during both the high-water and low-water states of the Amazon River hydrograph. Measurements included temperature, oxygen, ammonia, phosphate, and chlorophyll. In both lakes thermal stratification developed during the day and was eroded at night. During the low-water period when the lakes were shallow, nocturnal circulation extended to the lake bottom, whereas when the lakes were deeper (greater than about 5 m), circulation did not reach the bottom and an anoxic hypolimnion developed. During the low-water period, percent of oxygen concentrations were relatively high but always less than saturation. Low oxygen concentrations were observed during the high-water period. At all times nocturnal mixing supplied a significant amount of oxygen to the lake ecosystems. Nighttime upward mixing of recycled nitrogen and phosphorus also appeared to be important nutrient sources for algal productivity.     

An acetylenic mechanism-based inhibitor of dopamine beta-hydroxylase

The catalytic action of dopamine beta-hydroxylase on 1-phenyl-1-propyne results in concomitant loss of enzyme activity. At pH 5.5 and 25 degrees C, 1-phenyl-1-propyne inactivates dopamine beta-hydroxylase in a mechanism-based fashion. The inactivation rate is first-order, follows saturation kinetics, and is strictly dependent on catalysis (oxygen and ascorbate are essential). The inactivation rate of saturating 1-phenyl-1-propyne (kinact) increases from 0.08 to 0.22 min-1 when the oxygen saturation increases from 21 to 100%, respectively. Inactivation also requires a copper-containing catalytically competent enzyme. Tyramine and norepinephrine (respectively, substrate and product of the normal catalytic reaction) protect against inactivation, and no regain of enzyme activity occurs after prolonged dialysis. Experiments with ether-extracted incubation solutions (+/- enzyme) showed no difference in their gas chromatography-mass spectral patterns implying that inactivation of dopamine beta-hydroxylase by 1-phenyl-1-propyne occurs through a kinetic process with a partition ratio (kcat/kinact) equal to or near 1. Thus, this acetylenic substrate analog appears to be a very efficient mechanism-based inhibitor of dopamine beta-hydroxylase. We propose that inactivation of this enzyme by 1-phenyl-1-propyne proceeds by formation of a reactive intermediate that occurs prior to product formation and that alkylates an amino acid residue at the active site of the enzyme.     

Reactions of sugar nitro-alkenes with acetoacetic esters

3,4,5,6,7-Penta-O-acetyl-1,2-dideoxy-1-nitro-d-gluco-hept-1-enitol reacts with methyl acetoacetate in an unusual Michael reaction, giving the normal adduct (6), and a bicyclic derivative (9) that arises from quasi-dimerization of the former when a high concentration of the base is used. Acetylation of compound 9 gives the hydroxylamine O-acetate (10).From the reactions of 3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitro-d-galacto-hept-1-enitol with ethyl and tert-butyl acetoacetate, the normal adducts (7 and 8) were isolated. The structures of compounds 6 to 10 were established on the basis of their spectral properties (u.v., i.r., mass, and ¹H- and ¹³C-n.m.r.)     

Production of pectinases byAspergillus sp using differently pretreated lemon peel as the carbon source

Summary Aspergillus sp strains from decaying lemons were tested for extracellular pectinase production, testing differently pretreated lemon peel as the carbon source instead of pectin. It was found that the production of extracellular polygalacturonase was about the same and that of pectinesterase substantially higher when unwashed fresh lemon peel was used instead of pectin. The culture filtrate obtained showed a clarifying capacity similar to that of a commercial pectinase preparation, but the vitamin C of the juice was less affected by the treatment.     

Increased GH responsiveness to dopamine receptor stimulation in alcohol addicts during the late withdrawal syndrome

In humans the release of growth hormone (GH) elicited by dopamine (DA) and DA agonists may represent a reliable model to assess change in sensitivity of DA receptors. We now report that in chronic alcoholics, 4–7 days after the suspension of alcohol consumption, the increase of GH response to DA infusion was higher than that seen in non alcoholic volunteers. The specificity of this GH response to DA administration was demonstrated by the use of domperidone, a novel peripheral antagonist of DA receptors. These results suggest the development of hyper-responsiveness of DA receptors involved in the control of GH secretion in chronic alcoholics during the later phases of the “withdrawal syndrome”.