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PubMedDate not supplied

Glucose transport in Streptococcus mutans: preparation of cytoplasmic membranes and characteristics of phosphotransferase activity.

Cytoplasmic membranes from Streptococcus mutans were used to study phosphoenolpyruvate (PEP)-dependent glucose transport. The Km values for glucose and PEP were 0.3 and 0.4 mM. The system was sensitive to sulfhydryl reagents and detergents. The nonmetabolizable analogue 2-D-deoxyglucose was readily phosphorylated while alpha-methyl-glucose and 3-0-methylglucose were inefficiently derivatized. The fermentable sugars fructose, galactose, mannitol, and sorbitol were phosphorylated at reduced rates.

Cell Fractionation↗
PubMed2003

[Preparation of acellularized porcine heart valve and seeding of bovine aortic endothelial cells].

OBJECTIVE: To explore the possibility of detergent acellularized porcine heart valve serving as a scaffold for tissue engineering valve. METHODS: The porcine aortic valves were acellularized by use of trypsin-EDTA. Triton X-100, RNase and DNase treatment. Biomechanical characteristics of fresh valves and acellularized valve were tested; also fresh valves, acellularized valve and valves treated with method of bioprothetic treatment were implanted subcutaneously in rats; frequently seeded with bovine aortic endothelial cells(BAECs), and then cultured for 7 days. RESULTS: The acellularization procedure resulted in complete removal of the cellular components while the construction of matrix was maintained. The matrix could be successfully seeded with in vitro expanded BAECs, which formed a continuous monolayer on the surface. There is no significant difference of PGI2 secretion of BAECs between cells seeded onto the acellular leaflets and that onto the wells of 24-wells plate (P > 0.05). CONCLUSION: Acellularied porcine aortic valve can be applied as a scaffold to develop tissue engineering heart valve.

Animals↗
PubMed2006

Glycerate-oxidizing activity of glycolate oxidase from leaves of Spinacia oleracea.

Glycolate oxidase (GO) was purified to homogeneity from leaves of spinach (Spinacia oleracea). Through detecting the consumption of oxygen and the formation of hydrogen peroxide in the assay solution, it was found that GO could also oxidize glycerate, another metabolite in the photorespiratory pathway, and use FMN and FAD, but not riboflavin and lumiflavin, as its cofactors. The optimum reaction pH, Km for glycerate, k(cat) and activation energy of this oxidizing reaction were determined to be 8.0, 7.14 mmol/L, 1.04 s(-1) and 17.29 kJ/mol, respectively. Oxalate and pyruvate at 5.0 mmol/L could inhibit the glycerate-oxidizing activity by 34% and 26%, and oxalate acted as a competitive inhibitor of the glycerate oxidation reaction with a K(i) of 0.75 mmol/L. By the competition plotting with mixed-substrates, it was indicated that glycolate-oxidizing activity and glycerate-oxidizing activity of GO shared the same active site.

Alcohol Oxidoreductases↗
PubMed1991

Inactivation of enolase from carp (Cyprinus carpio) muscle by 2,3-butanedione.

Enolase from white muscle of carp (Cyprinus carpio) is inactivated by 2,3-butanedione in borate buffer. Magnesium ions as well as substrate--2-phosphoglycerate markedly altered the rate and extent of inactivation. The partially inactivated enzyme shows unaltered Km but decreased Vmax after 10 min incubation with butanedione, however after 60 min incubation the Km value increased 2.5 fold.

Animals↗
PubMed1991

Reconstitution of the phosphoglycerate transport protein of Salmonella typhimurium.

Operation of the phosphoglycerate transport protein (PgtP) of Salmonella typhimurium has been studied in proteoliposomes by using a technique in which membrane protein is solubilized and reconstituted directly from small volumes of cell cultures. When protein from induced cells was reconstituted into phosphate (Pi)-loaded proteoliposomes, it was possible to demonstrate a PgtP-mediated exchange of internal and external phosphate. For this homologous Pi:Pi antiport, kinetic analysis indicated a Michaelis constant (Kt) of 1 mM and a maximal velocity of 26 nmol/min mg of protein; arsenate inhibited with a Ki of 1.3 mM, suggesting that PgtP did not discriminate between these two inorganic substrates. Pi-loaded proteoliposomes also accumulated 3-phosphoglycerate and phosphoenolpyruvate, establishing for each of them a concentration gradient (in/out) of about 100-fold; phosphoenolpyruvate (Ki = 70 microM) rather than 3-phosphoglycerate (Kt = 700, Ki = 900 microM) was the preferred substrate for these conditions. We also concluded that such heterologous exchange was a neutral event, since its rate and extent were unaffected by the presence of a protonophore and unresponsive to the imposition of a membrane potential (positive or negative inside). In quantitative work, we found a stoichiometry of 1:1 for the exchange of Pi and 3-phosphoglycerate, and given an electroneutral exchange, this finding is most easily understood as the overall exchange of divalent Pi against divalent phosphoglycerate. These experiments establish that PgtP functions as an anion exchange protein and that it shares important mechanistic features with the Pi-linked antiporters, GlpT and UhpT, responsible for transport of glycerol 3-phosphate and hexose 6-phosphates into Escherichia coli.

Bacterial Proteins↗
PubMed1990

Steady-state kinetic properties of phosphoglycerate kinase of mung beans.

Steady-state kinetics of the action of mung bean phosphoglycerate kinase have been investigated using 3-phosphoglycerate and ATP as substrates in the presence of Mg2+ ions. Keeping a constant and high Mg2+ concentration and varying the concentration of one of the substrates (ATP or 3-phosphoglycerates) at several fixed concentrations of the other substrate (3-phosphoglycerate or ATP), the Km values of Mg.ATP2- and 3-phosphoglycerate were found to be 0.42 and 0.60 mM, respectively. These values are independent of the concentration of the other substrate. A limiting value of Vmax, where the enzyme is saturated with both the substrates, was found to be 39.4 mumoles product formed per min per mg enzyme protein. This corresponds to a turnover number equal to 31.5 sec-1 (for molecular weight of the enzyme equal to 48,000). If [Mg2+] and [ATP4-] are held equal and varied together at several fixed concentrations of 3-phosphoglycerate, deviations from Michaelis-Menten kinetics (non-linear Lineweaver-Burk plots) are observed at lower values of ATP4- and Mg2+ (less than 0.1 mM), giving rise to apparent sigmoidicity in the rate versus [ATP4-] plots. It has been suggested that the real substrate for this enzyme is the Mg.ATP2- complex (and not free ATP4-). The complex dissociates at lower values of [Mg2+] and [ATP4-]. The resulting disproportionate decrease in the concentration of the complex brings about a steeper fall in the rate of reaction than is required by the Michaelis-Menten equation, giving rise to an apparent sigmoidicity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

Model studies of the regulation of the Calvin photosynthesis cycle by cytosolic metabolites.

A kinetic model for photosynthetic carbohydrate formation in the chloroplast of C3 plants is presented which includes consideration of the interaction of the phosphate translocator of the chloroplast envelope with external reactants such as 3-phosphoglycerate, dihydroxyacetone phosphate, and glyceraldehyde 3-phosphate in addition to inorganic (ortho)phosphate. The model is shown to account satisfactorily for experimentally observed effects of such reactants on the rates of carbon dioxide fixation and starch production in isolated chloroplast. The predictions of the model with regard to the regulation of stromal processes of photosynthetic carbohydrate formation by cytosolic concentration variables have been examined. The results indicate that the cytosolic concentrations of metabolites that interact with the phosphate translocator represent important regulatory signals. Increasing levels of exported photosynthate (phosphoglycerates and triose phosphates) in the cytosol do not suppress the rate of photosynthetic carbon dioxide fixation, but redirects reaction flux such that starch production within the chloroplasts is favoured at the expense of a decreased rate of photosynthate export to the cytosol.

Carbon Dioxide↗
PubMed1990

Regulation of ACV synthetase: biosynthesis and action.

The biosynthesis of cephalosporins has been studied for almost 30 years. Development of cell-free systems began with the later enzymes of the pathway and, in recent years, moved to the early part of the pathway. The first enzyme, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase was one of most difficult to demonstrate in cell-free extracts. We recently developed a reproducible system from Cephalosporium acremonium (Banko et al., 1987) and similar activity has been found in Streptomyces clavuligerus (Jensen et al., 1988). With this assay, we have been able to study the regulation of ACV synthetase formation and action. Our results are summarized in this communication. Our comparison of the intracellular specific activities of the beta-lactam synthetases in both C. acremonium c-10 and S. clavuligerus NRRL 3585 indicates that ACV synthetase possesses the lowest activity and appears to be the rate-limiting step in the cephalosporin biosynthetic process. Since it is the initial enzyme in the biosynthetic pathway common to both penicillins and cephalosporins, this makes sense from a cellular economy viewpoint. It is therefore understandable that ACV synthetase would be subject to greater regulatory control than other steps.

Acremonium↗