Schistosoma mansoni: Inhibition of glucosephosphate isomerase and glycolysis by sugar phosphates

Glucosephosphate isomerase (EC 5.3.1.9) of Schistosoma mansoni is inhibited competitively by a number of tetrose, pentose, and hexose phosphates with inhibitor constant (K_i) values in the range of 0.5 to 400 μM. The most potent inhibitor is 5-phospho-d-arabinonate which resembles the cis-enediolate transition state intermediate of the reaction. These analogs were also found to be effective inhibitors of the production of lactate from glucose by suitably supplemented worm homogenates. The rank order of potency of inhibition of glycolysis was inversely related to the magnitudes of the K_i values for glucosephosphate isomerase. These K_i values were similar to those previously reported for mammalian glucosephosphate isomerase, suggesting similarities in the steric and electronic characteristics of the active sites of these isofunctional enzymes. This conclusion was further supported by the observed pH dependence of the inhibition by 5-phospho-d-arabinonate. Although glucosephosphate isomerase is not a rate-limiting enzyme of glycolysis, in the conventional sense, its selective inhibition could be of chemotherapeutic importance, in part because of the accumulation in glycolyzing systems of glucose 6-phosphate which is a potent feedback inhibitor of hexokinase.     

Changes in mouse brain diazepam receptor binding after phenobarbital administration

Specific ³H-diazepam binding was measured $\text{in vitro}$ in adult mouse (strain, Crl=CD-1) brain after four days of an inductive dose of phenobarbital pretreatment (i.p.). Sexual dimorphism was observed in ³H-diazepam brain binding, female mice had significantly higher benzodiazepine binding than males without any differences in apparent affinity constants (K_D). Phenobarbital pretreatment caused a significant decrease in the maximal number of binding sites (Bmax) as well as in dissociation rate constants in both sexes.     

Regulation of membrane peptides by the Pseudomonas plasmid alk regulon.

Pseudomonas putida strains carrying the plasmid alk genes will grow on n-alkanes. Induced alk+ strains contain membrane activities for alkane hydroxylation and dehydrogenation of aliphatic primary alcohols. P. putida cytoplasmic and outer membranes can be separated by sucrose gradient centrifugation after disruption of cells by either mild detergent lysis or passage through a French press. Both the membrane component of alkane hydroxylase and membrane alcohol dehydrogenase fractionated with the cytoplasmic membrane. Induction of the alk regulon resulted in the appearance of at least three new plasmid-determined cytoplasmic membrane peptides of about 59,000 (59K), 47,000 (47K), and 40,000 (40K) daltons as well as the disappearance of a pair of chromosomally encoded outer membrane peptides of about 43,000 daltons. The 40K peptide is the membrane component of alkane hydroxylase and the product of the plasmid alkB gene because the alkB1029 mutation altered the properties of alkane hydroxylase in whole cells, reduced its thermal stability in cell extracts, and led to increased electrophoretic mobility of the inducible 40K peptide. These results are consistent with a model for vectorial oxidation of n-alkanes in the cytoplasmic membrane of P. putida.     

Spontaneous frequency of a developmental mutant in Volvox

Two types of mutants, those resistant to the base analog 5-bromo-2′-deoxyuridine (BrdU) and somatic regenerator (SR) mutants, have been analyzed in Volvox carteri. In somatic regenerator mutants, the somatic cells which are normally terminally differentiated dedifferentiate and regenerate gonidia [Sessoms, A., and Huskey, R. J. (1973). Proc. Nat. Acad. Sci. USA70, 1335–1338; Starr, R. C. (1970). Develop. Biol. Suppl.4, 59–100]. The SR phenotype allows recovery of SR mutations arising in somatic cells, since such somatic cells would regenerate gonidia and give rise to mutant clones. Mutants of any phenotype other than SR can only be recovered if the mutation first appears in a gonidium. Since the somatic cells are 100-fold more numerous than reproductive cells (gonidia), we have determined the spontaneous frequency of both somatic regenerator mutants and mutations to BrdU resistance in order to determine if the SR mutation exerts its effect in the gonidium or in the somatic cell. The two frequencies were found to be nearly identical, suggesting that the SR mutation must first appear in a gonidium in order to be expressed.     

Galactose catabolism in Caulobacter crescentus.

Caulobacter crescentus wild-type strain CB13 is unable to utilize galactose as the sole carbon source unless derivatives of cyclic AMP are present. Spontaneous mutants have been isolated which are able to grow on galactose in the absence of exogenous cyclic nucleotides. These mutants and the wild-type strain were used to determine the pathway of galactose catabolism in this organism. It is shown here that C. crescentus catabolizes galactose by the Entner-Duodoroff pathway. Galactose is initially converted to galactonate by galactose dehydrogenase and then 2-keto-3-deoxy-6-phosphogalactonate aldolase catalyzes the hydrolysis of 2-keto-3-deoxy-6-phosphogalactonic acid to yield triose phosphate and pyruvate. Two enzymes of galactose catabolism, galactose dehydrogenase and 2-keto-3-deoxy-6-phosphogalactonate aldolase, were shown to be inducible and independently regulated. Furthermore, galactose uptake was observed to be regulated independently of the galactose catabolic enzymes.     

Reaction of uracil and thymine derivatives with sodium bisulfite. Studies on the mechanism and reduction of the adduct.

The rates and equilibria for the addition of sodium bisulfite to uracil, thymine, and their nucleosides have been studied for the pH range 3-9.5. The rate of addition for uracil is proportional to the concentration of sulfite ion and unionized uracil. The equilibrium constant (25 degrees C) for the reaction is (1.0 +/- 0.15) X 10(3) 1 - mol-1 for uracil and 0.62 +/- 0.03 1- mol-1 for thymine. A pH of 6-7, with a high bisulfite concentration is suggested for biochemical applications of the uracil reaction. The uracil reaction, which proceeds readily under physiological conditions and has a high equilibrium constant, may be a contributing cause of the biochemical effects of bisulfite and sulfur dioxide. Additional evidence on the structure of the thymine-bisulfite adduct has been obtained by nuclear magnetic resonance spectroscopy. This spectrum supports the assignment of structure as dihydrothymine-6-sulfonate. The uracil-bisulfite adduct is reduced by sodium borohydride to sodium 3-ureido-propanol-2-sulfonate. This reaction is suggested for the chemical modification of nucleic acids.     

In vitro translation and estradiol-17beta induction of Xenopus laevis vitellogenin messenger RNA.

Administration of estradiol-17beta to male Xenopus laevis induces synthesis and secretion by the liver of the egg yolk precursor protein vitellogenin. RNA extracted from livers of estradiol-17beta-treated Xenopus laevis directs the synthesis of the entire 200,000-dalton vitellogenin monomer in a cell-free protein synthesizing system derived from rabbit reticulocytes. Vitellogenin synthesized in vitro was isolated and quantitated by indirect immunoprecipitation and identified by comparison to authentic [14C]vitellogenin. The in vitro product and [14C]vitellogenin co-migrate on electrophoresis in sodium dodecyl sulfate-polyacrylamide gels and they exhibit identical immunoprecipitation curves. Xenopus laevis vitellogenin messenger RNA has a sedimentation coefficient of approximately 30 S in sucrose density gradients. It can be purified approximately 60-fold from cell RNA by poly(U)-Sepharose chromatography and therefore appears to contain a polyadenylate sequence. Vitellogenin mRNA and vitellogenin synthesis in vivo could not be detected in unstimulated male Xenopus laevis. The relative rate of vitellogenin synthesis and the level of vitellogenin mRNA were determined at various times following the administration of estradiol-17beta. Vitellogenin synthesis is maximal 12 days after estradiol-17beta administration when it comprises approximately 70% of cell protein synthesis. The level of vitellogenin mRNA and the intracellular rate of vitellogenin synthesis exhibit a close correspondence from 4 to 16 days after administration of estradiol-17beta.