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Biomedical subjects

R Serrano

Publications and source records attributed to R Serrano.

At least 163 records · Page 9Linked to original sources
PubMed1980

Effect of ATPase inhibitors on the proton pump of respiratory-deficient yeast.

Diethylstilbestrol and dicyclohexylcarbodiimide inhibit the ATPase of the plasma membranes and the proton-pumping activity of the cells in a respiratory-deficient mutant of Saccharomyces cerevisiae. The effects of the inhibitors in vivo seem to be specific because neither the proton permeability nor the ATPase levels of the cells are affected. These results indicate that the yeast plasma-membrane ATPase corresponds to the proton pump of the cells. The fact that both inhibitors of the ATPase delay the fall of ATP levels which follows a block of fermentation indicates that ATPase function is one of the major ATP-consuming pathways in yeast. In addition, diethylstilbestrol prevents the fall of ATP levels produced by dinitrophenol, suggesting that this fall was caused by partial dissipation of the proton gradient and consequent stimulation of the proton-pumping ATPase.

Adenosine Triphosphatases↗
PubMed1979

Anatomo-radiological considerations about lumbar discography. An experimental study.

An experimental study was undertaken to determine the origin of lumbar pain associated with degeneration of lumbar intervertebral disc by examining their innervation, vascularization, and stages of evolution. The study included the comparison of discography on patients with an experimental reproduction of this examination on cadavers.

Adolescent↗
PubMed1978

Characterization of the plasma membrane ATPase of Saccharomyces cerevisiae.

1. The distribution of ATPase and several marker enzymes was examined after differential and sucrose gradient centrifugation of yeast homogenates. 2. An ATPase activity not sensitive to oligomycin is found exclusively associated with a particulate fraction equilibrating at densities of 1.23-1.25. This particulate material shows the chemical and enzymatic characteristics of the yeast plasma membrane. 3. The pH optimum of the plasma membrane ATPase is 5.6, as compared with 8.5 for the mitochondrial ATPase. In addition to oligomycin, the enzyme is not sensitive to other inhibitors of the mitochondrial ATPase as azide, dicyclohexylcarbodiimide and the mitochondrial ATPase inhibitor protein. It is inhibited by p-chloromercuryphenyl sulfonate, fluoride, quercetin and by the antibiotic Dio-9 but is not affected by ouabain. 4. The plasma membrane ATPase shows a high affinity for ATP (Km = 0.1 mM) and is very specific for this compound, hydrolyzing other nucleotide triphosphates less than 25% as rapidly. No activity was detected with ADP. 5. The enzyme requires a divalent cation for activity and Mg2+ is the most effective. It is not significantly stimulated by K+ or bicarbonate and Ca2+ is inhibitory. 6. The activity cannot be assayed in intact cells unless they are permeabilized with toluene. This suggest that the active site is on the cytoplasmic side of the plasma membrane.

Adenosine Triphosphatases↗
PubMed1978

An ethnic comparison of self-esteem in Portuguese-, Mexican-, and Anglo-American pupils.

Three groups of Portuguese-, Mexican-, and Anglo-American boys and girls (N - 158) from 5th through 8th grade were compared in self-esteem. The results of the chi square test indicated that there were no significant differences between Mexican and Anglo Ss. However, significant differences were observed when the Portuguese Ss were compared to the other two groups. Here it was discovered that Portuguese boys--but not girls--had significantly higher self-esteem than all other Ss.

Child↗
PubMed1977

Energy requirements for maltose transport in yeast.

Maltose transport in yeast (Saccharomyces cerevisiae) is inhibited by uncouplers under conditions where the intracellular concentration of the sugar is lower than in the medium. The uncouplers did not deplete the ATP content of the yeast cells and a 50--100-fold reduction in ATP caused by antimycin and 2-deoxyglucose had no effect on maltose transport. In ATP-depleted cells, the maltose transported is partially hydrolyzed to glucose but not further metabolized and therefore a mechanism of transport involving phosphorylation can be discarded. One proton is cotransported with every maltose molecule. The fact that maltose transport is inhibited by KCl but not by NaCl, Tris-Cl or KSCN suggest that the electroneutrality during maltose and proton uptake can be maintained by the exit of K+ from the cells or by the entry of a permeable anion as SCN-. These results indicate that the translocation of maltose across the yeast plasma membrane is not dependent on ATP and is coupled to the electrochemical gradient of protons in this membrane. When this gradient is abolished by uncouplers, the transport system is not able to function even in favour of a concentration gradient of the sugar.

Adenosine Triphosphate↗
PubMed1976

6-phosphofructokinase (pyrophosphate). Properties of the enzyme from Entamoeba histolytica and its reaction mechanism.

The inorganic pyrophosphate-requiring 6-phosphofructokinase of Entamoeba histolytica has been further investigated. The molecular weight of the enzyme is approximately 83,000 and its isoelectric point occurs at pH 5.8 to 6.0. The divalent cation requirement for reaction was explored. In the direction of fructose 6-phosphate formation half-maximal rate required 500 muM magnesium ion; in the direction of fructose bisphosphate formation 8 muM magnesium ion sufficed. ATP, PPi, polyphosphate, acetyl phosphate, or carbamyl phosphate cannot replace PPi as phosphate donor for the conversion of fructose 6-phosphate to fructose bisphosphate. In the direction of fructose 6-phosphate formation arsenate can replace orthophosphate. Isotope exchange studies indicate that little or no exchange occurs between Pi and PPi or between fructose 6-phosphate and fructose bisphosphate in the absence of a third substrate. These findings appear to rule out phosphoenzyme formation and a ping-pong reaction mechanism. PPi, Pi, and fructose bisphosphate are competitive inhibitors of fructose bisphosphate, PPi, and fructose 6-phosphate, respectively. This argues against an ordered mechanism and suggests a random mechanism. Fructose 6-phosphate and Pi were noncompetitive with respect to each other indicating the formation of a dead end complex. These product inhibition relationships are in accord with a Random Bi Bi mechanism.

Diphosphates↗
PubMed1976

Purification and properties of the proton-translocating adenosine triphosphatase complex of bovine heart mitochondria.

1. The proton-translocating adenosine triphosphatase (ATPase) of bovine heart mitochondria was highly purified by extraction of submitochondrial particles with cholate, fractionation with ammonium sulfate, and sucrose gradient centrifugation in the presence of methanol, deoxycholate, and lysolecithin. 2. The preparation had a very low content of phospholipids, respiratory components, and adenine nucleotide transporter. The ATPase activity (14 o 16 micromoles/min/mg at 30 degrees) was dependent on addition of phospholipids. The purified enzyme was reconstituted with phospholipids, coupling factor 1 (F1), and the oligomycin sensitivity-conferring protein (OSCP) yielding vesicles with highly active 32Pi-ATP exchange (up to 260 nanomoles/min/mg at 30 degrees), and a proton pump driven by ATP. Site III oxidative phosphorylation was reconstituted when purified cytochrome oxidase was included. 3. The 32Pi-ATP exchange of the reconstituted vesicles was sensitive to both rutamycin and dichylohexylcarbodiimide but the ATPase activity was sensitive to rutamycin and not to dicyclohexylcarbodiimide. 4. In sodium dodecyl sulfate-acrylamide gel scans of the complex, the subunits of F1, OSCP, and three other major bands with apparent molecular weights of 32,000, 23,000, and about 11,000 were noted. Three other minor bands with estimated molecular weights of 80,000, 70,000, and 52,000 were also detected. These bands apparently represent residual trace amounts of respiratory components. Quantitative assays of individual respiratory components revealed between 0 and 3% contamination. 5. We conclude that the rutamycin-sensitive ATPase complex functions as a reversible ATP-driven proton pump.

Adenosine Triphosphatases↗
PubMed1974

Glucose transport in Entamoeba histolytica.

That the uptake of glucose by the parasitic amoeba Entamoeba histolytica occurs by an equilibrative transport system is supported by the following observations. 1. The rate of glucose uptake is several orders of magnitude greater than the uptake by pinocytosis. 2. The uptake of glucose exhibits saturation kinetics, with K(m)=1.6mm and V(max.) ranging from 2 to 5mumol/min per ml of cells at 37 degrees C. 3. The glucose analogues 2-deoxyglucose, 3-O-methylglucose and d-xylose are transported by the glucose system although with much less affinity. Competitive inhibition was observed between pairs of substrates, with K(i) values for any sugar closely coincident with the corresponding K(m). 4. d-Xylose, a sugar not metabolized by the cells, equilibrated with 80% of the amoebal cell water. 5. Cells equilibrated with xylose exhibited countertransport of this sugar against its concentration gradient when another substrate was added to the medium. 6. Blocking of glycolysis by iodoacetate or F(-) has no immediate effect on transport. The presence of a glucose-transport system in E. histolytica contrasts with the situation found in the non-parasitic amoeba, where pinocytosis seems to be the only mechanism of solute uptake.

Binding, Competitive↗