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M L Campo

Publications and source records attributed to M L Campo.

27 records · Page 2Linked to original sources
PubMed1987

Effect of nucleotides and inhibitory anions on mitochondrial ATPase. Its pH dependence.

The effect of pH on the sensitivity of F1-ATPase as well as mitochondrial ATPase activity to nucleoside diand triphosphates and to inhibitory anions such as cyanate and thiocyanate, has been studied. The results obtained show that nucleotides could act as activators or inhibitors of the ATPase hydrolytic activity depending on pH, substrate concentration, and binding of the enzyme to the membrane. The effect of those nucleotides which activate the hydrolysis of ATP-Mg2+ was more pronounced beyon the optimum pH corresponding to each of the three catalytic sites of the enzyme, whereas those which are inhibitors had a lower effect above this value. The sensitivity to the inhibitory anions decreased with increasing pH values; the decrease in the inhibitory effect was sharper when approaching the optimum pH value. These data are in agreement with the existence in mitochondrial ATPase of two different regulatory sites, one being specific for binding nucleotides, and another for anions. Both of them showed a different response upon changes of pH.

Adenosine Triphosphatases↗
PubMed1985

Protonmotive force and photophosphorylation in single swollen thylakoid vesicles.

Swollen vesicles generally 40 micron in diameter were prepared from spinach chloroplasts. These vesicles appear to originate from thylakoids. The present study reports results obtained with individual vesicles using micromanipulative procedures. The electric potential across the membrane was measured with microelectrodes and the pH of the internal space was calculated from the fluorescence of the pH indicator pyranine. The individual vesicles photophosphorylate as measured with luciferin-luciferase. Impalement with microelectrodes did not affect the ability of individual vesicles to photophosphorylate. However, there was no significant membrane potential either with continuous illumination or light flashes. In contrast, we found a delta pH of 3.7 under photophosphorylative conditions and the incubation with the appropriate buffers blocked photophosphorylation presumably by preventing formation of a pH gradient. We propose that, in these vesicles, the membrane potential plays no role in photophosphorylation, whereas a pH gradient is obligatory.

Adenosine Triphosphate↗
PubMed1984

Assay of ATP synthesis using single giant mitochondria.

Two assays of the capacity of single giant mitochondria or mitoplasts to phosphorylate ATP from Pi and ADP have been developed. One depends on the placement of a single mitochondrion next to a glycerinated myofibril, by micromanipulation. With the appropriate controls, contraction of the myofibril serves as an indication of ATP synthesis. The other assay similarly requires the isolation of one single mitochondrion but the assay of ATP synthesized uses the luciferin-luciferase reaction with a conventional photometric system. With the latter, we found that either impalement with microelectrodes or electrophoretic microinjection of two dyes, Lucifer Yellow CH or pyranine , into the inner space have no effect on the phosphorylative capacity of mitochondria or mitoplasts. The electric potential across the mitochondrial membrane was monitored during the assay and found to be small and generally positive inside.

Adenosine Triphosphate↗
PubMed1984

Protonmotive force in giant mitochondria.

The accompanying communication [Eur. J. Biochem. 141 (1984) 1-4] indicates that the microinjection of the pH fluorescent indicator pyranine (8-hydroxy-1,2,6- pyrenesulfonate ) into giant mitochondria or mitoplasts does not affect their ability to carry out oxidative phosphorylation. The dye can therefore be used as a quantitative indicator of internal mitochondrial pH. We found that activation of metabolism in rotenone-inhibited giant mitochondria by the addition of succinate produces an internal pH change corresponding to a pH shift of 0.3 to the alkaline range, approximately the same value found previously for conventional rat liver mitochondria.

Animals↗
PubMed1983

Three catalytic sites in mitochondrial ATPase.

Kinetic data obtained after determining the hydrolytic activity of ATPase from rat liver in preparations where the enzyme had been purified, or in mitochondria, strongly suggest the existence of three different catalytic sites with different affinity for the substrate. The results obtained when measuring the ATPase activity at different substrate concentrations, and in the presence of the inhibitors KOCN or KSCN, or of the activators dinitrophenol and bicarbonate, show that the binding of these compounds to a regulatory site or sites affects in a different degree the hydrolytic activity of each catalytic site.

Adenosine Triphosphatases↗
PubMed1980

Effect of pH on the sensitivity of mitochondrial ATPase to free ATP, ADP and anions.

The pH activity curves of the hydrolyzing activity of ATPase obtained with rat liver mitochondria or with the isolated F1-ATPase at three different substrate concentrations exhibited different optimum pH values. At 0.06 mM ATPMg2+ maximal activity was reached at pH 7; at 0.67 mM ATPMg2+ the optimum value was around 8; and at 3 mM ATPMg2+ between pH 8.2 and 9. These results suggest the presence of different catalytic sites in the enzyme with different affinities for the substrate and different optimum pH values. The sensitivity to the activating anions dinitrophenol and bicarbonate decreased with increasing pH values; the decrease in the activating effect was sharper when approaching the optimum pH value at any of the three substrate concentrations tested. These results might indicate that either OH-, dinitrophenol, or bicarbonate could compete for a regulatory site or sites in ATPase. The activating effect of free ATP on the hydrolyzing activity of isolated F1-ATPase was found to be dependent on the pH of the medium. The activating effect was more pronounced above the optimum corresponding to each of the three ATPMg2+ concentrations used, whereas the inhibitory effect of ADP was more manifest at pH values below that optimum point.

Adenosine Diphosphate↗
PubMedDate not supplied

An arginine regulated gamma-guanidobutyrate ureahydrolase from tench liver (Tinca tinca L.).

A gamma-guanidobutyrate ureahydrolase isolated from tench liver has been characterized. Some of its physicochemical properties like pH effect and thermal stability resemble those of arginases, however it shows some peculiarities that makes it different from arginases and other amidino hydrolases. Thus cation requirement is not as strong as in arginases, and the Km value for gamma-guanido-butyric acid (230 +/- 25 mM) is shifted to a lower value (45 +/- 5 mM) by 5 mM arginine. The possible regulatory role of arginine on gamma-guanidobutyrate ureahydrolase activity is discussed.

Animals↗
PubMedDate not supplied

Kinetics and inhibition by some aminoacids of lactating rat mammary gland arginase.

Some kinetic and regulatory properties of lactating rat mammary gland arginase were studied. At pH 7.4, i.e. at near-physiological conditions, there was evidence of inhibition by excess of substrate, with a Km value of 9.5 mM, slightly lower than the value of 18 mM observed at pH 9.8 (maximum enzyme activity). A study was also made of the effects of proline, ornithine, lysine and certain branched-chain aminoacids on enzyme activity: lactating rat mammary gland arginase was strongly and competitively inhibited by lysine, ornithine and valine, with Ki values of 1.2 mM, 1.1 mM and 3.6 mM, respectively. Other aminoacids (proline, isoleucine and leucine) also inhibited lactating rat mammary gland arginase, although to a lesser extent.

Amino Acids↗