Scavenging of superoxide radical by ascorbic acid

Using acetaldehyde and xanthine oxidase as the source of suPeroxide radical, the second order rate constant for the reaction between ascorbic acid and superoxide radical was estimated to be 8.2 X 10⁷ M^-1 s^-1. In rats, the average tissue concentration of ascorbic acid was of the order of 10^-3 M and that of superoxide dismutase was of the order of 10^-6 M. So, taking together both the rate constants and the tissue concentrations, the efficacy of ascorbic acid for scavenging superoxide radical in animal tissues appears to be better than that of suPeroxide dismutase. The significance of ascorbic acid as a scavenger of superoxide radical has been discussed from the point of view of the evolution of ascorbic acid synthesizing capacity of terrestrial vertebrates.     

Localization of the gene for a third G protein β-subunit to mouse chromosome 6 near Raf-1

The large family of signal transducing proteins known as G proteins are heterotrimers that dissociate into an independent α-subunit and βγ-subunit complex after ligand binding or other stimulation. For Gα, at least 30 distinct sequences representing 10 different classes have been identified. On the other hand, cDNAs for only three Gβ-subunit genes have been isolated so far. All three of the Gβ genes have been chromosomally mapped in the human, but only two in the mouse. Using a human retinal cDNA for the third G protein β-subunit, we have mapped the corresponding gene, termed Gnb-3, to mouse Chromosome 6 with somatic cell hybrids and have positioned it distal to but near the marker Raf-1 by analysis of the progeny of three genetic crosses.     

Studies on modulation of the effects of colchicine by L-cysteine using bone marrow of Swiss mice

Colchicine (COL) elevates the frequency of micronucleated polychromatic erythrocytes (PE), the ratio of normochromatic to polychromatic erythrocytes (N/PE) and the frequency of large PE due to spindle disruption. Simultaneous i.p. injection of L-cysteine (CYS) does not influence the effects of COL while if administered 1 h prior to COL, CYS suppresses the N/PE ratio and frequency of large PE but not the frequency of micronucleated PE elevated by COL. Preincubation of CYS with COL at 37 degrees C for 1 h results in a significant decrease in all the COL effects. The modulatory effect of exogenous CYS appears to be due to its competition with the endogenous tubulin cysteine residues for interacting with COL.     

Effect of dibutyryl cyclic AMP on lipid synthesis in Microsporum gypseum

The influence of intracellular levels of cAMP on the lipid synthesis of Microsporum gypseum has been examined by exogenous supplementation of dibutyryl cAMP and its activators/inhibitors. Incorporation of [14C]acetate into various lipid fractions of M. gypseum was markedly enhanced in the presence of dibutyryl cAMP and its modulators, probably as a consequence of increased intracellular cAMP levels, which, in turn, affected the lipid biosynthesis. Increased activities of phosphatidic acid phosphatase, glycerol kinase, ethanolamine kinase and choline kinase in the presence of these additives supports the enhanced synthesis of phospholipids and suggests that lipid biosynthesis is being controlled by cAMP in M. gypseum.     

Alkaloid production byClaviceps sp. SD-58; Involvement of phosphatase isozymes

Simultaneous reduction in alkaloid yield and level of phosphatases by high concentrations of phosphate was observed inClaviceps sp. SD-58. Tryptophan-induced culture showed an increase in alkaloid yield and the level of phosphatases. Phosphate caused repression of both acid phosphatase (isoenzyme I) and alkaline phosphatase (isoenzymes III and V).     

Floral induction by gibberellic acid in Impatiens balsamina,a qualitative short-day plant

Summary In the qualitative short-day plant Impatiens balsamina, gibberellic acid (GA₃) not only promoted the formation of floral buds in response to suboptimal photoinductive conditions and reduced the number of SD cycles that are required for their development into flowers, but also caused initiation of floral buds under non-inductive photoperiods. In plants treated with repeated applications of GA₃, the floral buds developed into flowers irrespective of whether the apex was left intact or was removed. In those that received a single application of GA₃ the floral buds developed into flowers only in decapitated plants.     

Surfactant-induced breakthrough effects during the operation of two-phase biocatalytic membrane reactors

Surface-active components, both reactants and products, are frequently encountered in two-phase, aqueous-organic, biocatalytic reactions, When such reaction are carried out in a membrane reactor, employing a membrane selectively wetted by one of the two reactants, changes in the content of these surfactants- as a consequence of the progress of the reaction-can lead to wetting transitions at the two membrane-liquid interfaces as a result of adsorption of the tenside. This can lead to a decrease in the pressure required to cause the, initially, nonwetting phase to break through the membrane. Such effects render difficult the operation of two-phase membrane bioreactors. Hence, it is necessary to make a careful selection of the membrane material and type by considering factors such as UF versus MF and low MWCO versus high MWCO to enable the reactor to be operated without breakthrough, but without significantly compromising the reaction rates that can be maintained.The phenomena leading to breakthrough effects are discussed in this paper, and experimental results for the hydrolysis of ethyl laurate by lipase from Candida rugosa in a batch flat sheet membrane reactor are presented with the reactor operated with a variety of membranes. An experimental result showing the decrease in the pressure required to cause breakthrough of the organic phase (for the system ethyl laurate-lauric acid-water) as the content of the highly surface-active lauric acid in the organic phase is increased is also presented for an asymmetric, hydrophilic meta-aramid ultrafiltration membrane. (c) 1994 John Wiley & Sons, Inc.