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The transport system for malic acid present in Schizosaccharomyces pombe cells, growing in batch culture on several carbon sources, has been studied. It was found that the dicarboxylic acid carrier of S. pombe is a proton-dicarboxylate symporter that allows uphill transport and accumulation as a function of delta pH with the following kinetic parameters at pH 5.0: Vmax = 0.1 nmol of total malic acid s-1 mg (dry weight) of cells-1 and Km = 1.0 mM total malic acid. Malic acid uptake (pH 5.0) was accompanied by disappearance of extracellular protons, the uptake rates of which followed Michaelis-Menten kinetics as a function of the acid concentration. The Km values calculated as the concentrations either of anions or of undissociated acid, at various extracellular pH values, pointed to the monoanionic form as the transported species. Furthermore, accumulated free acid suffered rapid efflux after the addition of the protonophore carbonyl cyanid m-chlorophenyl hydrazone. These results suggested that the transport system was a dicarboxylate-proton symporter. Growth of cells in a medium with glucose (up to 14%, w/v) and malic acid (1.5%, w/v) also resulted in proton-dicarboxylate activity, suggesting that the system, besides being constitutive, was still active at high glucose concentrations. The following dicarboxylic acids acted as competitive inhibitors of malic acid transport at pH 5.0: D-malic acid, succinic acid, fumaric acid, oxaloacetic acid, alpha-ketoglutaric acid, maleic acid and malonic acid. In addition, all of these dicarboxylic acids induced proton movements that followed Michaelis-Menten kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol at concentrations above 12% (v/v) in mineral medium with glucose and with ammonium as the only nitrogen source induced rapid inactivation of the ammonium transport system in the strain IGC 3507 of Saccharomyces cerevisiae terminating protein synthesis. Subsequently, when glucose was present, the glucose transport system was irreversibly inactivated. This two-step mechanism may play a decisive role when ethanol stops fermentation by S. cerevisiae, before all the fermentable sugar has been consumed.

Ethanol, isopropanol, propanol, and butanol enhanced thermal death in Saccharomyces cerevisiae by increasing DeltaSdouble dagger, the entropy of activation of thermal death while DeltaHdouble dagger, the enthalpy of activation, was not significantly affected. The relation between DeltaSdouble dagger and alkanol concentration was linear with a different slope for each alkanol: DeltaS(double dagger) (X) = DeltaS(double dagger) (0) + C(A) (E)X, where X is the alkanol concentration and C(A) (E) the entropy coefficient for the aqueous phase defined as increase in entropy of activation per unit concentrations of the alkanol. C(A) (E) was correlated with the lipid-buffer partition coefficients of the alkanols while C(M) (E), the entropy coefficient for the lipid phase, was nearly identical for the four alkanol and averaged 37.6 entropy units per mole of alkanol per kilogram of membrane. As predicted by these results, the specific death rates (K(d)) at constant temperature were an exponential function of the alkanol concentration and behaved in agreement with the following equation: In K(X) (d) = In K(0) (d) + (C(A) (E)/R)X, where R is the gas constant. It was concluded that the alkanols enhanced thermal death through nonspecific action on membrane structure.

Fourteen gastric ulcer patients were submitted to treatment with Cimetidine. They were endoscopically controlled before the beginning of treatment and at the third and sixth week. In the first phase of the investigation, cimetidine was given in a dosage of 1.0 g/day. At the end of the 3rd week, those patients who showed a reduction of less than 50% on the size of the ulcer had the cimetidine doses increased to 1.6 g/day. The second phase started with nine patients which healed at the end of the six weeks. These patients were randomly allocated to two groups in a double blind trial involving cimetidine (600 mg/day) or placebo for 12 weeks. At the end of this period, the patients were submitted to an endoscopic control. Two patients in the placebo group had a recurrence of their ulcers. This did not happen to any of the patients taking cimetidine. Two and a half months after stopping their maintenance treatment, two patients of the cimetidine group had a recurrence of their lesions.

Ethanol, isopropanol, propanol and butanol enhanced the passive influx of protons into deenergized cells of Saccharomyces cerevisiae. The influx followed first-order kinetics with a rate constant that increased exponentially with the alkanol concentration. The exponential enhancement constants increased with the lipid solubility of the alkanols, which indicated hydrophobic membrane regions as the target sites. While the enhancement constants were independent of pH over the range tested (3.3-5.0), the rate constants decreased linearly with increasing extracellular proton concentration, indicating the presence of an additional surface barrier against proton penetration, the effectiveness of which increased with protonation. The alkanols affected the acidification curves of energized yeast suspensions in such a way that the final pH values were linear functions of the alkanol concentrations. These results were consistent with a balance between active and passive proton movements at the final pH, the exponential enhancement constants calculated from the slopes being nearly identical with those obtained with deenergized cells. It was concluded that passive proton influx contributes to the kinetics of acidification in S. cerevisiae and that uncoupling contributes to the overall kinetics of alkanol-inhibited secondary active transport across the yeast plasma membrane.

Acetic acid at concentrations as may occur during vinification and other alcoholic yeast fermentations induced death of glucose-grown cell populations of Saccharomyces cerevisiae IGC 4072 at temperatures at which thermal death was not detectable. The Arrhenius plots of specific death rates with various concentrations of acetic acid (0-2%, w/v) pH 3.3 were linear and could be decomposed into two distinct families of parallel straight lines, indicating that acetic acid induced two types of death: (1) High enthalpy death (HED) predominated at lower acetic acid concentrations (> 0.5%, w/v) and higher temperatures; its enthalpy of activation (DeltaH( not equal)) approached that of thermal death (12.4 x 10(4) cal/mol); (2) Low enthalpy death (LED) predominated at higher acetic acid concentrations and lower temperatures with DeltaH( not equal) of 3.9 x 10(4) cal/mol. While the DeltaH( not equal) values for HED induced by acetic acid were similar with those reported earlier for HED induced by other fermentation endproducts, the values for the entropy coefficients were different: 127-168 entropy units mol(-1)L for acetic acid as compared with 3.6-5.1 entropy units mol(-1)L for ethanol, which agreed with experimental results indicating that acetic acid is over 30-times more toxic than ethanol with respect to yeast cell viability at high process temperatures.

Saccharomyces cerevisiae IGC4072 grown in lactic acid medium transported lactate by an accumulative electroneutral proton-lactate symport with a proton-lactate stoichiometry of 1:1. The accumulation ratio measured with propionate increased with decreasing pH from ca. 24-fold at pH 6.0 to ca. 1,400-fold at pH 3.0. The symport accepted the following monocarboxylates (Km values at 25 degrees C and pH 5.5): D-lactate (0.13 mM), L-lactate (0.13 mM), pyruvate (0.34 mM), propionate (0.09 mM), and acetate (0.05 mM), whereas apparently a different proton symport accepted formate (0.13 mM). The lactate system was inducible and was subject to glucose repression. Undissociated lactic acid entered the cells by simple diffusion. The permeability of the plasma membrane for undissociated lactic acid increased exponentially with pH, and the diffusion constant increased 40-fold when the pH was increased from 3.0 to 6.0.