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Biomedical subjects

R L Veech

Publications and source records attributed to R L Veech.

At least 127 records · Page 7Linked to original sources
PubMed1974

Equilibrium relations between the oxidation-reduction reactions and the adenosine triphosphate synthesis in suspensions of isolated liver cells.

1. The redox state of cytochrome c, cytochrome a and the mitochondrial NAD couple, and the phosphorylation state of the adenine nucleotides, were measured in suspensions of isolated rat liver cells. 2. The DeltaG for the transfer of two electrons from the mitochondrial NAD to the cytochrome c couple is calculated to be 104kJ (24.8kcal). 3. The DeltaG associated with the synthesis of ATP at the measured phosphorylation state is calculated to be 95kJ (22.7kcal)/2mol of ATP. 4. The near equality of DeltaG of the electron-transport process and DeltaG required for ATP synthesis indicates near-equilibrium between the mitochondrial respiratory chain and the extramitochondrial phosphorylation state. 5. The existence of near-equilibrium in the coupled reactions implies that the respiratory activity depends on the ratio [ATP]/[ADP][P(i)] and not on the concentrations of the individual reactants. 6. If the overall system of oxidative phosphorylation is at near-equilibrium, all intermediary reactions must also be at equilibrium. Hence if the intramitochondrial and extramitochondrial phosphorylation states are indeed different, it follows that any differences in the activities of ATP, ADP and P(i) must be coupled to ion gradients and/or potentials across the inner mitochondrial membrane in such a way that translocation occurs without loss of free energy. 7. The metabolic state of the mitochondria in the cell can be defined by the turnover number of the cytochromes, the cytoplasmic phosphorylation state, and the oxidation-reduction potential of the NAD couple, rather than by the availability of ADP, substrate and O(2).

Acetoacetates↗
PubMed1974

The increased rate of ethanol removal from blood of clofibrate-treated rats.

After ethanol injection similar metabolite changes were found in livers of clofibrate-treated and non-treated rats. The rate of ethanol removal from blood of clofibrate-treated rats was increased by 50%, but this was directly proportional to the increased liver size caused by clofibrate. No other difference needs to be postulated to explain the increased rate of ethanol removal from blood.

Animals↗
PubMed1974

The concentration and control of cytoplasmic free inorganic pyrophosphate in rat liver in vivo.

The concentration of cytoplasmic free pyrophosphate was calculated in freeze-clamped livers of rats from the measured concentration of reactants and K(eq.) of the UDP-glucose pyrophosphorylase reaction (UDP-alpha-d-glucose 1-phosphate uridylyltransferase, EC 2.7.7.9). The K(eq.) of the UDP-glucose pyrophosphorylase reaction was redetermined at 38 degrees C, pH7.0, I=0.25mol/l and free [Mg(2+)]=1mm, and was 4.55 in the direction of glucose 1-phosphate formation. The activity of UDP-glucose pyrophosphorylase in rat liver was between 46 and 58mumol of glucose 1-phosphate formed/min per g fresh wt. in the four dietary conditions studied. A fluorimetric assay with enzymic cycling was developed for the measurement of glucose 1-phosphate in HClO(4) extracts of rat liver. The calculated free cytoplasmic PP(i) concentration in nmol/g fresh wt. of liver was 2.3+/-0.3 in starved, 3.8+/-0.4 in fed, 4.9+/-0.6 in meal-fed and 5.2+/-0.4 in sucrose-re-fed animals. These values agree well with recently determined direct measurements of total PP(i) in rat liver and suggest that there is not a large amount of bound or metabolically inert PP(i) in rat liver. The cytoplasmic [ATP]/[AMP][PP(i)] ratio is 10(3) times the cytoplasmic [ATP]/[ADP][P(i)] ratio and varies differently with dietary state. The reaction PP(i)+H(2)O-->2P(i) catalysed by inorganic pyrophosphatase (EC 3.6.1.1) does not attain near-equilibrium in vivo. PP(i) should be considered as one of the group of small inorganic ions which is metabolically active and capable of exerting a controlling function in a number of important metabolic reactions.

Adenosine Diphosphate↗
PubMed1973

Cyclic adenosine monphosphate, metabolites, and phosphorylase in neural tissue: a comparison a methods of fixation.

Fixation of rat brain tissue by freeze-blowing, microwave irradiation, immersion of whole rats in liquid nitrogen, and decapitation into liquid nitrogen indicates that postmortem changes in metabolites and enzyme forms are minimal in freeze-blown brains. Cyclic adenosine monophosphate levels are lowest in microwave-irradiated brains, which has been interpreted by some investigators to indicate rapid fixation and minimal anoxia. However, the changes in phosphocreatine, adenosine triphosphate, lactate, and phosphorylase clearly demonstrate that fixation by freeze-blowing or immersion in liquid nitrogen more closely approximate the state in vivo.

Adenosine Triphosphate↗
PubMed1973

Phenylketonuria: phenylalanine inhibits brain pyruvate kinase in vivo.

The hypothesis that brain damage in phenylketonuria is related to inhibition of pyruvate kinase by phenylalanine was examined in rat brain in vivo. One hour after a single injection of phenylalanine into the rat, the brains were removed and completely frozen in less than a second. The concentration of phenylalanine in the brain was comparable to that found in phenylketonuric patients. Changes in brain glycolytic intermediates were consistent with inhibition of pyruvate kinase in vivo. The inhibition of pyruvate kinase was apparently compensated for by an increase in phosphoenolpyruvate; no decrease in adenosine triphosphate or creatine phosphate was found.

Adenosine Diphosphate↗
PubMed1973

The acute action of ammonia on rat brain metabolism in vivo.

1. Acute NH(4) (+) toxicity was studied by using a new apparatus that removes and freezes the brains of conscious rats within 1s. 2. Brains were removed and frozen 5min after intraperitoneal injection of ammonium acetate (2-3min before the onset of convulsions). Arterial [NH(4) (+)] rose from less than 0.01 to 1.74mm at 4-5min. The concentrations of all glycolytic intermediates measured, except glucose 6-phosphate, were increased by the indicated percentage above the control value as follows: glucose (by 41%), fructose 1,6-diphosphate (by 133%), dihydroxyacetone phosphate (by 164%), alpha-glycerophosphate (by 45%), phosphoenolpyruvate (by 67%) and pyruvate (by 26%). 4. Citrate and alpha-oxoglutarate concentrations were unchanged and that of malate was increased (by 17%). 5. Adenine nucleotides and P(i) concentrations were unchanged but the concentration of creatine phosphate decreased slightly (by 6%). 6. Brain [NH(4) (+)] increased from 0.2 to 1.53mm. Net glutamine synthesis occurred at an average rate of 0.33mumol/min per g. 7. The rate of brain glucose utilization was measured in vivo as 0.62mumol/min per g in controls and 0.81mumol/min per g after NH(4) (+) injection. 8. The arteriovenous difference of glucose and O(2) increased by 35%. 9. No significant arteriovenous differences of glutamate or glutamine were detected. Thus, although much NH(4) (+) was incorporated into glutamine the latter was not rapidly released from the brain to the circulation. 10. Plasma [K(+)] increased from 3.3 to 5.4mm. 11. The results indicate that NH(4) (+) stimulates oxidative metabolism but does not interfere with brain energy balance. The increased rate of oxidative metabolism could not be accounted for only on the basis of glutamine synthesis. We suggest that increased extracellular [NH(4) (+)] and [K(+)] decreased the resting transmembrane potential and stimulated Na(+),K(+)-stimulated adenosine triphosphatase activity thus accounting for the increased metabolic rate.

Ammonia↗
PubMed1973

Ethanol administration and the relationship of malonyl-coenzyme A concentrations to the rate of fatty acid synthesis in rat liver.

1. The effect of ethanol on liver fatty acid synthesis was studied in vivo in 24h-starved and ;meal-fed' rats (i.e. fed for 3h per day and not ad libitum). 2. In the fed animal (3)H(2)O was incorporated into fat at a rate of 0.46mumol of C(2) units/min per g wet wt. of liver. Administration of either ethanol (3.2g/kg) or equicaloric amounts of glucose had no effect on the rate of (3)H(2)O incorporation into lipid. 3. In the 24h-starved animal, administration of the same dose of ethanol produced an increase in the rate of (3)H(2)O incorporation from 0.06 to 0.12mumol of C(2) units/min per g fresh wt. after 3h whereas [malonyl-CoA] increased from 0.006 to 0.009mumol/g. Glucose given in amounts equicaloric to ethanol was significantly more lipogenic, increasing both the (3)H(2)O incorporation from 0.06 to 0.20mumol of C(2) units/min per g and the malonyl-CoA content from 0.006 to 0.013 mumol/g wet wt. at 3h. 4. The decrease in the redox state of free cytoplasm NAD or NADP couples or the changes in content of citrate, glucose 6-phosphate and pyruvate of liver after ethanol administration had no measurable effect on the rate of fatty acid synthesis in vivo. 5. Under the conditions of the experiments there was no significant difference, among any of the groups, in the activity of liver fatty acid synthetase measured in vitro. A double-reciprocal plot of the rate of (3)H(2)O incorporation and the total tissue malonyl-CoA concentrations showed a striking relationship. It has been concluded that the rate of fatty acid synthesis in vivo is determined principally by the V(max.) of fatty acid synthetase and the concentration of free malonyl-CoA. 6. It has also been concluded that under the conditions of the present study, the synthesis of fatty acids de novo is unlikely to be an important factor in the increased liver lipid content associated with ethanol administration.

Acetyl-CoA Carboxylase↗