D-glucosamine propanedithioacetal, an efficient chiral auxiliary in beta-lactam chemistry.

The synthesis of some monocyclic beta-lactams (monobactams) by the Staudinger reaction using D-glucosamine propanedithioacetal as chiral auxiliary is reported. The influence of several radicals at C3, C4, and C1' (sugar moiety) as well as other structural aspects are considered in relation to the antielastase activity.     

Cytochemical localization of alkaline phosphatase and ouabain-sensitive K+-dependent p-nitrophenylphosphatase activities in brain capillaries of the newt

The ultrastructural localization of alkaline phosphatase and K+-NPPase was investigated in brain capillaries of newt by a cytochemical study using whole brain perfusion. The alkaline phosphatase activity was present in both luminal and antiluminal membranes of the endothelial cells. By contrast, the K+-NPPase was located only in antiluminal membranes of the brain capillaries. This distinct enzymatic distribution suggested that the luminal and antiluminal membranes are functionally different. The role of alkaline phosphatase and K+-NPPase in the blood brain barrier is discussed.     

Acute effects of insulin and glucagon on hepatic casein kinase 2 in adult fed rats: correlation of the effects on casein kinase 2 with the changes in glycogen synthase activity

Administration of insulin to adult fed rats caused an inactivation of hepatic casein kinase 2 as determined by the decrease in the activity ratio measured at a low (0.1 mg/ml) and a high (1.0 mg/ml) concentration of beta-casein. Maximal inactivation occurred 45 min after injection and the dose for half-maximal effect was 44 micrograms/kg. The effect of insulin was due to an increase in the apparent Km value for the protein substrate but the magnitude of the effect depended on the substrate used, decreasing in the order beta-casein greater than glycogen synthase much greater than whole casein. The activation of casein kinase 2 by glucagon (M. Pérez, J. Grande, and E. Itarte (1988) FEBS Lett. 238, 273-276) was also more marked with beta-casein and glycogen synthase than with whole casein. A good correlation was observed between the time- and dose-dependent activation of glycogen synthase and inactivation of casein kinase 2 promoted by insulin. Similarly, the inactivation of glycogen synthase by glucagon correlated with the activation of casein kinase 2 caused by this hormone. The possible involvement of casein kinase 2 on the mechanism(s) through which these hormones control hepatic glycogen synthase is discussed.     

Chromosome abnormalities in tuberous sclerosis

Summary In fibroblasts cultured from biopsies of the skin lesions of six patients with tuberous sclerosis (TS) there was a variable but consistent degree of karyotypic variation. Premature centromere disjunction (PCD) of all or part of the chromosomes, micronuclei, an increased incidence of breaks, dicentric chromosomes and the presence of polyploid metaphases were found in all cultures. The PCD was of the type encountered in Roberts syndrome and its frequency varied from 8% to 30%. In metaphases with PCD of one and of two chromosomes, the chromosome involved were identified, and chromosome 3 was involved 21 times among 59 chromosomes with PCD. Chromosome 3 tends to be preferentially involved in dicentric formation. In lymphocyte cultures from the same patients there were no metaphases with PCD, but there was a slight increase of breaks and the presence of dicentric chromosomes, also involving chromosome 3. Polyploid metaphases were increased in some of the cases. Karyotypic variation can be considered a cellular phenotypic characteristic of TS in fibroblasts cultured from the skin lesions, and its type indicates disturbances in the mechanics of centromere division and of chromosome distribution at cell division.     

Amphetamine and chlorpromazine modify cerebral insulin levels in rats

Rats treated with chlorpromazine (CPZ) (1 mg/kg/day i.p.) experienced a marked decline in cerebral insulin levels (0.057 +/- 0.01 ng/g wet weight) with respect to a control group (0.38 +/- 0.05 ng/g wet weight), while rats given D-amphetamine bitartrate (AMPH) chronically (20 mg/kg/day p.o.) showed a rise in cerebral insulin (0.55 +/- 0.04 ng/g wet weight). Combined treatment with both drugs at the same dosages produced lower cerebral insulin levels (0.46 +/- 0.10 ng/g wet weight) than in the AMPH animals. In the groups of rats treated with CPZ and with AMPH + CPZ, there was a slight elevation in serum insulin levels. Serum glucose values did not vary.     

A comparison of net and gross rates of oxygen production as a function of light intensity in some natural plankton populations and in a Synechococcus culture

In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,¹⁸O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500–800 µE m^–2 s^–1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [P_max;sensu Platt et al (1980) JMar. Res., 38, 687–701] the rates of ‘light’respiration were 3 times greater. In two other communities,with high rates of dark respiration relative to P_maxthe ratesof ‘light’ respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of ‘light’ respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m^–2 s^–1). Therates of ¹⁴C production were also measured as a function oflight intensity The photosynthetic quotients, based on ¹⁴C productionrates and gross oxygen production rates, average 1 9     

Effects of nitrogen deprivation on the ATP-sulphurylase and O-acetylserine sulphydrylase activities of mesophyll protoplasts and bundle sheath strands of maize leaves

In maize leaves nitrogen (N)-deprivation induced a significant decline of chlorophyl and total N contents. On the contrary, sulphur (S) content increased with N-deprivation. The activities of ATP-sulphurylase and O-acetylserine sulphydrylase also decreased with N-deprivation, but ATP-sulphurylase activity was more sensitive than O-acetylserine sulphydrylase activity to N-deficiency both in whole leaf extracts and in isolated leaf cells. Finally, N-deprivation induced higher changes in activity of the two enzymes in mesophyll protoplasts than in bundle sheath strands. This research was supported by Consiglio Nazionale delle Ricerche-Special grant I.P.R.A.-Subproject 1. Paper N. 73.     

Kinetic properties of hydrogenase isolated from Desulfovibrio vulgaris (Hildenborough)

Hydrogenase of Desulfovibrio vulgaris shows nonlinear kinetics in hydrogen production with both the natural electron carrier, cytochrome c3, and the artificial donor, methyl viologen semiquinone. Increasing concentrations of salt progressively inhibit the hydrogen production, as do increasing amounts of dimethylsulfoxide (Me2SO). Hydrogen consumption activity does not change up to 30% (v/v) of Me2SO. Preincubation in Me2SO up to 55% (v/v) does not affect the hydrogen uptake or production. The production activity of the enzyme shows an optimum around pH 6. When plotted as a function of redox potential the activity can be fitted to a Nernst equation with n = 1. Midpoint potentials calculated at various values follow approximately the hydrogen electrode to pH 6. Thereafter, there is a shift of about 40 mV to higher redox potentials.