HUMANGGP:003739 - FACTA Search

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Query: HUMANGGP:003739 (CO2)
48,959 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The intracellular pH (pHi) of squid giant axons has been measured using glass pH microelectrodes. Resting pHi in artificial seawater (ASW) (pH 7.6-7.8) at 23 degrees C was 7.32 +/- 0.02 (7.28 if corrected for liquid junction potential). Exposure of the axon to 5% CO2 at constant external pH caused a sharp decrease in pHi, while the subsequent removal of the gas caused pHi to overshoot its initial value. If the exposure to CO2 was prolonged, two additional effects were noted: (a) during the exposure, the rapid initial fall in pHi was followed by a slow rise, and (b) after the exposure, the overshoot was greatly exaggerated. Application of external NH4Cl caused pHi to rise sharply; return to normal ASW caused pHi to return to a value below its initial one. If the exposure to NH4Cl was prolonged, two additional effects were noted: (a) during the exposure, the rapid initial rise in pHi was followed by a slow fall, and (b) after the exposure, the undershoot was greatly exaggerated. Exposure to several weak acid metabolic inhibitors caused a fall in pHi whose reversibility depended upon length of exposure. Inverting the electrochemical gradient for H+ with 100 mM K-ASW had no effect on pHi changes resulting from short-term exposure to azide. A mathematical model explains the pHi changes caused by NH4Cl on the basis of passive movements of both NH3 and NH4+. The simultaneous passive movements of CO2 and HCO3-cannot explain the results of the CO2 experiments; these data require the postulation of an active proton extrusion and/or sequestration mechanism.
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PMID:Intracellular pH transients in squid giant axons caused by CO2, NH3, and metabolic inhibitors. 0 60

We have used a stopped flow rapid reaction pH apparatus to investigate the carbamate equilibrium in glycylglycine solutions and in three biological tissues, human plasma, sheep muscle, and sheep brain, as well as to investigate the kinetics of carbamate formation in glyclyglycine solution and in human plasma. The rapid reaction apparatus was equipped with a pH sensitive glass electrode in order to follow the time course of pH from 0.005 to 100 s after rapid mixing of a solution of amine or protein and CO2. Two phases of the pH curve were observed: a fast phase representing carbamate formation, and a slow phase due to the hydration of CO2 which was uncatalyzed since a carbonic anhydrase inhibitor was added to the biological solutions. From the time course of pH change during the fast phase K2, the R-NH2 ionization constant, and Kc, the carbamate equilibrium constant as well as the velocity constant for the formation of carbamate, ka could be calculated from data at different pH and pCO2. The carbamate formed in glycylglycine solutions over a wide range of pH and pCO2 was found consistent with the theory of carbamate formation and with published data. At ionic strength 0.16 and 37 degrees pK is 7.67. pKc 4.58. The heat of the carbamate reaction (deltaH) was calculated to be -3.2 kcal/mol between 20 degrees and 37 degrees. Kt of glycylglycine depends quantitatively on ionic strength as predicted by the Debye-Huckel theory. With ionic strength 0.16 ku was found to be 2,500 M1 S1 at 37 degrees. The activation energy of carbamate formation is 6.7 kcal/mol. Carbamate measurements in human plasma at pCO2 from 38 to 359 Torr. pH from 6.9 to 8.3, temperature 37 degrees, and ionic strength 0.15 provided evidence that two kinds of amino groups participate in carbamate formation. From the equilibrium constants computed for the two species they could be identified as alpha- and epsilon-amino groups. On the basis of a protein molecular weight of 69.000. 0.6 alpha-amino groups/molecule with pKz=7.0 and pKc=4.2, and 5.9 epsilon-amino groups/molecule with pKz=9.0 and pKc=4.3 contribute to carbamate formation. The velocity constant ka was estimated to be 4,950 M1 S1 for the alpha-amino groups and 13,800 M1 S1 for the epsilon-amino groups. Under physiological conditions (pCO2=40 Torr. pH=7.4). The concentration of carbamate in plasma is 0.6 mM and the half-time of carbamate formation is 0.05 s. In extracts prepared from sheep brain at 37 degrees pH=7 and pCO2=35 Torr. the carbamate formation was estimated to be 0.8 mM. With pCO2=70 Torr and the same pH and temperature the carbamate concentration in muscle approximates 0.3 mM and increases to 7 mM as pH rises to 8. It is concluded that, as in plasma, a considerable number of epsilon-amino groups appear to be available for carbamate formation in these tissues.
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PMID:The carbamate reaction of glycylglycine, plasma, and tissue extracts evaluated by a pH stopped flow apparatus. 0 79

Ammonia production from glutamine was studied in slices from non-acidotic and acidotic rat kidneys. Slices from non-acidotic kidneys made 53% as much ammonia from D-glutamine as from L-glutamine during the initial 15 min of incubation. Thereafter the production rate from the L-isomer accelerated while that from the D-isomer remained constant. The accelerated rate of ammonia production from L-glutamine was dependent upon tissue swelling since prevention of swelling reduced the production rate. Swelling activates the mitochondrial glutaminase I pathway as evidenced by the rise in ammonia produced per glutamine utilized ratio as well as by the accelerated rate of CO2 production derived from the oxidative disposal of glutamin's carbon skeleton. Cortical slice swelling activates the mitochondrial pathway in a manner not unlike that seen in vivo during chronic acidosis and may reflect increased permeability to glutamine. Acidotic rat kidneys are not swollen in vivo while cortical slices initially produce 4-fold more ammonia than do non-acidotic slices. After 15 min, this 4-fold difference in total ammonia production drops to only a 2-fold difference due to the swelling-induced activation of the mitochondrial pathway. Consequently, slice swelling obliterates the important fact that ammonia production by the mitochondrial pathway is 15-fold greater in acidotic than in non-acidotic kidneys.
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PMID:Ammonia production and pathways of glutamine utilization in rat kidney slices. 1 Sep 71

NH3 production by renal cortical mitochondria was studied under conditions of metabolic acidosis induced in vivo and with pH manipulations of the media bathing mitochondria from normal rats. A HCO3- medium equilibrated with O2 and CO2 was utilized with glutamine concentrations of either 10 or 0.5 mM. With chronic acidosis NH3 production increased significantly at either substrate concentration. Similar results were obtained with rotenone in the media, both with chronic acidosis and with acidosis of 3 h duration, indicating that increased glutamine entry and/or phosphate-dependent glutaminase (PDG) activity accounts for the increased ammoniagenesis. In contrast to acidosis induced in vivo, mitochondria from normal rats subjected to a diminution in medium pH, either by manipulation of HCO3 concentration or PCO2, significantly decrease NH3 production. Mitochondrial studies with rotenone, as well as studies of solubilized PDG, suggest that a low pH diminishes NH3 production by directly altering PDG activity. Furthermore, regardless of the specifics of the mechanism, these studies indicate that adaptation to metabolic acidosis is not the immediate, direct result of a change in pH.
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PMID:Effect of pH on ammonia production by renal mitochondria. 1 62

Resting cells of Bacteroides melaninogenicus fermented L-[14C]aspartate as a single substrate. The 14C-labeled products included succinate, acetate, CO2, oxaloacetate, formate, malate, glycine, alanine, and fumarate in the relative percentages 68, 15, 9.9, 2.7, 1.8, 1.0, 0.7, 0.5, and 0.06, respectively, based on the total counts per minute of the L-[14C]aspartate fermented. Ammonia was produced in high amounts, indicating that 96% of the L-aspartate fermented was deaminated. These data suggest that L-aspartate is mainly being reduced through a number of intermediate reactions involving enzymes of the tricarboxylic acid cycle to succinate. L-[14C]asparagine was also fermented by resting cells of B. melaninogenicus to form L-aspartate, which was subsequently, but less actively, fermented.
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PMID:Fermentation of L-aspartate by a saccharolytic strain of Bacteroides melaninogenicus. 1 13

This paper demonstrates the formation of "active CO2" (CO2-P), a precursor of carbamoyl phosphate (CP), with frog liver carbamoyl-phosphate synthetase. Absence of ammonia is essential for the demonstration by pulse incubation with H14CO3- of CO2-P. Adenosine triphosphate (ATP) and acetylglutamate are required for the synthesis of CO2-P, which is highly unstable in aqueous solutions (t1/2 = 0.75 s at 24 degrees C at neutral pH). In the absence of ammonia, CO2-P attains rapidly a steady-state level, which depends on the concentration of ATP and HCO3-. The "apparent KM'S" are approximately equal to those found for the adenosine triphosphate (ATPase) activity of the enzyme. The maximum level of CO2-P is limited by the amount of enzyme, and approximates 4 mol of intermediate/mol of enzyme. The unprotonated form of ammonia seems to be the species reacting with CO2-P to produce CP. The reaction of CO2-P and NH3 is very fast (rate constant kn = 8 x 10(4) M-1 S-1) and does not consume free ATP. Therefore, the 2 mol of ATP necessary for CP synthesis binds or reacts with the enzyme and/or CO2 prior to reaction with NH3. The reaction of CO2-P with NH3 also takes place in acetone under conditions at which the enzyme is not active, suggesting little or no assistance from enzyme catalysis or that a part of the catalytic site is "frozen" by the solvent in the active conformation. In the light of these and other findings, a new scheme is proposed for the mechanism of frog liver carbamoyl-phosphate synthetase and some considerations are made on the chemical nature of the intermediate and on the possible evolutionary significance of the reaction of CO2-P with NH3 in acetone.
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PMID:Mechanism of mitochondrial carbamoyl-phosphate synthetase: synthesis and properties of active CO2, precursor of carbamoyl phosphate. 1 11

A new enzyme which catalyzes the oxidation of the side chain of tryptophan and other indole derivatives, has been purified to apparent homogeneity from Pseudomonas and crystallized. The overall purification was about 25-fold with a yield of 4.5%. The purified enzyme was apparently homogeneous as judged by polyacrylamide gel electrophoresis. The molecular weight estimated by gel filtration was approximately 280,000 and sedimentation coefficient (S20,w) was 11 by sucrose density gradient ultracentrifugation. The absorption spectra indicated that the enzyme was a hemoprotein. The purified enzyme was shown to catalyze the reaction in which 1 mol each of NH3 and CO2 was formed at the expense of 1 mol each of L-tryptophan and molecular oxygen. Neither peroxidase nor catalase activity was detected in the purified enzyme and no formation of H2O2 was observed during the enzyme reaction. The product(s) of the reaction was unstable but was converted to and was identified as its stable quinoxaline derivative, 2-(3-indolyl)quinoxaline, in the presence of o-phenylenediamine. These results indicate that the product of the reaction was 3-indolylglycoaldehyde or 3-indolylglyoxal. A variety of other indole derivatives such as D-tryptophan, 5-hydroxyl-L-tryptophan, tryptamine, serotonin, melatonin, N-acetyl-L-tryptophan, N-acetyl-L-tryptophanamide, 3-indoleacetamide, 3-indolelactic acid, 3-indolepropionic acid, 3-indoleethanol, and skatole were also substrates.
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PMID:Crystalline hemoprotein from Pseudomonas that catalyzes oxidation of side chain of tryptophan and other indole derivatives. 1 95

1. The intracellular pH (pHi) of surface fibres of the mouse soleus muscle has been measured in vitro using recessed-tip pH-sensitive microelectrodes. 2. In 5% CO2 and pH 7-40, the mean pHi was 7-07 +/- 0-007 (S.E. of mean) at 37 degrees C and 7-23 +/- 0-01 at 28 degrees C. The difference between these tow values is the same as the change in neutral pH between 37 and 28 degrees C. 3. Alteration of the CO2 level at constant external pH caused a biphasic change in pHi with a rapid displacement followed by a slower partial recovery. Because the recovery was incomplete, different stable pHi values were recorded at different CO2 levels, the higher the CO2 the lower the pHi. The differences in pHi were highly significant both at 37 and 28 degrees C. 4. Alteration of the CO2 level at constant external pH also changed the membrane potential (Em), an increase in CO2 leading to an increased Em. The dependence of Em on the CO2 level was much smaller in the fast-twitch muscle, extensor digitorum longus, than in soleus. 5. Changing external pH, either by alteration of the bicarbonate or CO2 level of the Ringer solution, caused pHi to change by a mean 38-7% of the external pH change. The change in pHi was accomplished about 10 times more rapidly, and in the same direction, by altering CO2 than by altering the bicarbonate. 6. Application of external NH3 and NH+4 caused a rapid intracellular alkalinization followed by a slower acidification. On removal of external NH3 and NH+4, there was a large and rapid acdification, followed by a fairly rapid recovery in pHi. 7. The size of the pHi changes occurring on alteration of the CO2 level at both constant external pH and constant external bicarbonate, and on removal of external NH3 and NH+4, suggests a non-CO2 buffering power of 45m-equiv H+ ions/pH unit per litre and a constant-CO2 buffering power of 58 m-equiv H+ ions/pH unit per litre. The buffering power was apparently unaffected by a change in temperature between 37 and 28 degrees C. 8. It was concluded that H+ ions are not passively distributed across the muscle cell membrane, and that the pHi is closely controlled by the active transport of H+, OH- or HCO-3 ions.
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PMID:Micro-electrode measurement of the intracellular pH and buffering power of mouse soleus muscle fibres. 1 40

Administering D-aldosterone, 7 microgram 100 g-1, to rats results in a marked rise in ammonium excretion and metabolic alkalosis. Increased ammonium excretion is not related to either a significant elevation in potassium excretion nor to hypokalemia. Consequently, potassium depletion does not appear to be the causative factor in the aldosterone-stimulated ammonium excretion. Isolated kidneys from aldosterone-treated rats, perfused with 1 mM L-glutamine, produced twice as much ammonia from glutamine as did controls. Ammonia production per glutamine extracted increased from 1.33 +/- 0.07 in control to 1.79 +/- 0.08 in kidneys from hormone-treated rats, suggesting stimulation of the mitochondrial glutaminase I-glutamate dehydrogenase pathway; this was supported by a proportional rise in production of glucose and CO2, end products of glutamine's carbon skeleton. Consequently, aldosterone-stimulated renal ammonia production, by specifically activating the mitochondrial pathway, leads to the elimination of hydrogen ions in the form of urinary ammonium excretion and an ensuing metabolic alkalosis.
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PMID:Influence of aldosterone on renal ammonia production. 1 22

9-Aminoacridine has been used to monitor the intrathylakoid pH of photosynthetically competent intact chloroplasts. Values obtained from 9-aminoacridine accumulation in the chloroplasts must be corrected for light-dependent binding of 9-aminoacridine to the thylakoid membranes. During nitrite reduction by intact chloroplasts, the intrathylakoid proton concentration increased. It decreased somewhat during CO2 reduction. However, low concentrations of uncoupling amines such as NH3 or cyclohexylamine, which rapidly penetrated the chloroplast envelope and decreased the intrathylakoid proton concentration, failed to reduce, and actually stimulated, rates of CO2-dependent oxygen evolution even under rate-limiting light. In contrast, low concentrations of carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) OR NIGERICIN, WHICH INHIBITED CO2 reduction, even appeared to increase the intrathylakoid proton concentration. As indicated by measurements of the 515 nm signal of the chloroplasts, the light-induced membrane potential was not much affected by low concentrations of the uncoupling amines, but was decreased by FCCP and by high concentrations of the amines. Even in the presence of high concentrations of NH4C1, ATP/ADP ratios of illuminated chloroplasts remained far above the ratios observed in the dark. In contrast, low concentrations of FCCP were sufficient to reduce ATP/ADP ratios to the dark value even under high intensity illumination. The observations are difficult to explain within the framework of the chemiosmotic hypothesis as presently discussed.
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PMID:CO2 reduction by intact chloroplasts under a diminished proton gradient. 1 73

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