Nucleic acid relationships among Acholeplasma species.

3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically.     

Monosomy 21: a new case confirmed by in situ hybridization

Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation.     

Development of gastric sensitivity to histamine in the rat

Sensitivity of the developing rat stomach to histamine (HA) was examined on isolated gastric mucosae of rats of various ages from the fetal to adult periods. Spontaneous acid secretion in mu eq/h.cm2 occurred at all the ages studied, at a basal rate of 0.45 +/- 0.07 in fetuses to 0.22 +/- 0.03 (day 5), 0.11 +/- 0.04 (day 10), 0.12 +/- 0.04 (day 12), 0.22 +/- 0.08 (day 16) and 0.33 +/- 0.04 (adults). In the fetal rats as in the adults, marked responses to respectively 10(-5) and 10(-4) M HA were demonstrated. The H2-receptor antagonist cimetidine diminished HA-induced secretion by 66 and 57% in fetuses and adults respectively. Between these two stages (from days 5 to 12), basal secretion and the response to HA dropped significantly. On day 21 of gestation, as well as on the critical days 5 and 12 after parturition, db-cAMP (10(-4) M) caused maximal stimulation of acid secretion. These results indicate that the development of responsiveness to HA in the rat is biphasic. They suggest that after birth, the H2-receptor adenylate cyclase system undergoes major modifications which might lead to the complete lack of responsiveness to HA by day 12.     

The stimulus-secretion coupling of amino acid-induced insulin release metabolic interaction L-asparagine and L-leucine in pancreatic islets

1. Because L-asparagine augments insulin release evoked by L-leucine, the metabolism of these two amino acids was investigated in rat pancreatic islets. 2. L-Leucine inhibited the uptake and deamidation of L-asparagine, but failed to exert any obvious primary effect upon the further catabolism of aspartate derived from exogenous asparagine. 3. L-Asparagine augmented the oxidation of L-leucine, and effect possibly attributable to activaion of 2-ketoisocaproate dehydrogenase. 4. The association of L-asparagine and L-leucine exerted a sparing action on the utilization of endogenous amino acids, so that the integrated rate of nutrients oxidation was virtually identical in the sole presence of L-leucine and simultaneous presence of L-asparagine and L-leucine, respectively. 5. It is proposed that the enhancing action of L-asparagine upon insulin release evoked by L-leucine is attributable to an increased generation rate of cytosolic NADPH rather than any increase in nutrients oxidation.     

Sulphydryl and Disulphide Levels in Protein Fractions from Hydrated and Dry Leaves of Resurrection Plants

Significant changes in sulphydryl (‘SH’) and disulphide(‘SS’) levels during air-drying in leaves of ‘resurrection’plants (whose protoplasm survives dehydration) stemmed mainlyfrom protein turnover effects. No significant changes were foundin the SH, SS levels in leaves of the desiccation sensitivespecies Sporobolus pyramidalis following air-drying. The three tolerant species studied differed in the directionof change. Some data were consistent with Levitt's SH, SS hypothesis:increases in protein-SS levels in Sporobolus stapfianus (desiccationtolerant) were consistent with a stabilization of new proteinby SS bonds; lower reactivity of protein-SH in the tolerantspecies Talbotia elegans (which on the other hand has decreasedprotein-SS) is consistent with a second mechanism of decreasingprotein denaturation proposed in Levitt's hypothesis. Evidence of some conversion of SH to SS in the soluble proteinsof Xerophyta viscosa (a tolerant species) would on Levitt'shypothesis indicate an injurious process. Some degree of proteindenaturation might be indicated by partial inactivation of thesoluble enzyme ribulose bisphosphate carboxylase in this species,and loss of some soluble isoenzymes (peroxidase and alkalinephosphatase). An apparent lack of SH conversion to SS in thesensitive species Sporobolus pyramidalis was not consistentwith the SH, SS hypothesis. Resurrection plants, Sporobolus pyramidalis, Sporobolus stapfianus, Talbotia elegans, Xerophyta viscosa, drought resistance, desiccation tolerance, protein turnover, sulphydryl groups     

An inexpensive photosynthetic irradiance sensor for ecological field studies

The design and characteristics of inexpensive and simply constructed equal-energy response photosynthetic irradiance sensors is described for use particularly where several cells are required in comparative ecological studies either above or below water. The dimensions of the sensors can be changed proportionally to suit different applications or components. The response of the sensor to irradiance at varying angles corresponds very closely to that required by the cosine law. The sensor is comparatively insensitive to other environmental variables in field use and gave a stable output; the long term drift was proportional to electrical output but in continuous use, drift is regular and could reach -0.08 year^-1 of the total. The spectral range and cosine response is discussed in comparison to other more expensive (x 5–10) commercially available, sensors and to local standards.     

Genes for the biosynthesis of spinosyns: applications for yield improvement in Saccharopolyspora spinosa

Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the final step in the biosynthesis — the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly. Journal of Industrial Microbiology & Biotechnology (2001) 27, 399–402. Received 31 May 2001/ Accepted in revised form 09 July 2001     

Suppression of A-type potassium current in pyramidal neurons of the rat hippocampus, induced by pinacidil and its fluorine derivatives

With the use of a patch-clamp technique in the whole-cell configuration, we studied the effects of pinacidil and its fluorine derivatives on A-type potassium current (I _A) through the membrane of pyramidal neurons of the rat hippocampus. Hydrogen peroxide (10 mM) exerted no influence on the rate of inactivation ofI _A; therefore, this current is probably mediated by Shal Kv4.2 potassium channels. Pinacidil demonstrated the properties of a weakI _A blocker: in the 500 μM concentration it blocked about 45% of the current, while 50 μM of pinacidil fluorine derivatives were capable of blocking up to 30% ofI _A. The effects of pinacidil and its derivatives showed no dependence on the stimulating potential. A similar pattern of the effects of pinacidil fluorine derivatives, which are an order of magnitude stronger than those of pinacidil itself, allows us to suppose that the imine nitrogen of the tested compounds is significantly more involved in the molecular interaction with the site of an A-type potassium channel than the pyridine nitrogen.