Gluconeogenesis in perfused chicken kidney. Effects of feeding and starvation.

1. Starvation for 48 hr doubled the rate of gluconeogenesis from lactate and pyruvate in perfused chicken kidney, but did not change the rate of production of glucose from malate, succinate, or alpha-ketoglutarate. 2. Amino-oxyacetate and D-malate inhibited the production of glucose from lactate and from pyruvate by 55% in each case. Quinolinate reduced the production of glucose from lactate and from pyruvate by 50% in both fed and starved chickens, but had no effect on the production of glucose from intermediates in the citric acid cycle. 3. Starvation increased the rate of formation of mitochondrial phosphoenolpyruvate from pyruvate, but had no effect on the rate of formation of mitochondrial phosphoenolpyruvate from malate.

Lactate metabolism in the perfused rat hindlimb.

A preparation of isolated rat hindleg was perfused with a medium consisting of bicarbonate buffer containing Ficoll and fluorocarbon, containing glucose and/or lactate. The leg was electrically prestimulated to deplete partially muscle glycogen. The glucose was labelled uniformly with 14C and with 3H in positions 2, 5 or 6, and lactate uniformly with 14C and with 3H in positions 2 or 3. Glucose carbon was predominantly recovered in glycogen, and to a lesser extent in lactate. The 3H/14C ration in glycogen from [5-3H,U-14C]- and [6-3H,U-14C]-glucose was the same as in glucose. Nearly all the utilized 3H from [2-3H]glucose was recovered as water. Insulin increased glucose uptake and glycogen synthesis 3-fold. When the muscle was perfused with a medium containing 10 mM-glucose and 2 mM-lactate, there was little change in lactate concentration. 14C from lactate was incorporated into glycogen. There was a marked exponential decrease in lactate specific radioactivity, much greater with [3H]- than with [14C]-lactate. The 'apparent turnover' of [U-14C]lactate was 0.28 mumol/min per g of muscle, and those of [2-3H]- and [3-3H]-lactate were both about 0.7 mumol/min per g. With 10 mM-lactate as sole substrate, there was a net uptake of lactate, at a rate of about 0.15 mumol/min per g, and the apparent turnover of [U-14C]lactate was 0.3 mumol/min per g. The apparent turnover of [3H]lactate was 3-5 times greater. When glycogen synthesis was low (no prestimulation, no insulin), the incorporation of lactate carbon into glycogen exceeded that from glucose, but at high rates of glycogen deposition the incorporation of lactate carbon was much less than that of glucose. Lactate incorporation into glycogen was similar in fast-twitch white and fast-twitch red muscle, but was very low in slow-twitch red fibres. We find that (a) pyruvate in muscle is incorporated into glycogen without randomization of carbon, and synthesis is not inhibited by mercaptopicolinate or cycloserine; (b) there is extensive lactate turnover in the absence of net lactate uptake, and there is a large dilution of 14C-labelled lactate from endogenous supply; (c) there is extensive detritiation of [2-3H]- and [3-3H]-lactate in excess of 14C utilization.

Relationships between phosphoenolpyruvate synthesis and glutamine formation in isolated chicken liver mitochondria.

The rate of phosphoenolpyruvate (PEP) and glutamine (Gln) formation was measured under different conditions in isolated chicken liver mitochondria. Glutamate (Glu) added as a sole substrate in high concentrations (30 mM) to the incubated mitochondria is preferentially metabolized to Gln, but Asp and PEP are also formed. Glu (10 mM) inhibited the rate of PEP formation from malate by about 25%. The effect was potentiated by NH4Cl (10 mM). Neither Glu nor NH4Cl affected the rate of PEP formation from malate by isolated guinea-pig liver mitochondria. Methionine S-sulfoximine, an inhibitor of Gln synthetase, did not reverse the inhibitory effect of Glu of PEP formation from malate in chicken liver mitochondria. The data are discussed in terms of possible interrelationships between uricogenesis and gluconeogenesis in chicken liver.

Studies on the mechanism of action of the hypoglycemic agent, 2-(3-methylcinnamylhydrazono)-propionate (BM 42.304).

A new hypoglycemic agent, 2-(3-methylcinnamylhydrazono)-propionate MCHP (BM 42.304) was shown to be an inhibitor of the transfer of long-chain fatty acids across the mitochondrial inner membrane. The following data support this conclusion: the drug, at already 5 microM, inhibited ketogenesis from oleate but not from octanoate in the perfused guinea-pig liver; likewise, ketogenesis from L-(-)-palmitoylcarnitine and palmitoyl-CoA + L-(-)-carnitine, but not from octanoate, was depressed in isolated guinea-pig liver mitochondria. Oxigraphic measurements of the oxygen uptake by isolated mitochondria showed that the drug impaired oxygen uptake with the long-chain fatty acid derivatives but not with octanoate. Finally, in vivo effects of the drug such as hypoketonemia and an increased concentration of free fatty acids in blood are in agreement with the above formulated mechanism of action. A comment is given on the relationships between fatty acid oxidation and gluconeogenesis in the guinea-pig liver.

A simple procedure for the synthesis of [32P]phosphoenolpyruvate via the pyruvate kinase exchange reaction at equilibrium.

A one step procedure is presented for the preparation of [32P]phosphoenolpyruvate from [gamma-32P]ATP using pyruvate kinase. The reaction is carried out at chemical equilibrium and involves only an exchange of isotope between ATP and phosphoenolpyruvate. The initial phosphoenolpyruvate/ATP ratio in the reaction mixture determines the degree of 32P incorporation into phosphoenolpyruvate when isotopic equilibrium is achieved.

Development of fatty acid oxidation in neonatal guinea-pig liver.

The capacity of foetal and neonatal liver to oxidize short-, medium- and long-chain fatty acids was studied in the guinea pig. Liver mitochondria from foetal and newborn animals were unable to synthesize ketone bodies from octanoate, but octanoylcarnitine and palmitoylcarnitine were readily ketogenic. The ketogenic capacity at 24 h after birth was as high as in adult animals. Hepatocytes isolated from term animals were unable to oxidize fatty acids, but at 6 h after birth production of 14CO2, acid-soluble products and acetoacetate from 1-14C-labelled fatty acids was 40-50% of the rates at 24 h. At 12 h of age these rates had already reached the 24 h values and did not change during suckling in the first week of life. The activities of hepatic fatty acyl-CoA synthetases, which were minimal in the foetus or at term, increased to maximal values in 12-24 h. The data show that the capacity for beta-oxidation and ketogenesis develops maximally in this species during the first 6-12 h after birth, and appears to be partly dependent on the development of fatty acid-activating enzyme.

Interrelationships between gluconeogenesis and uricogenesis in chicken liver.

1. Experiments performed on isolated hepatocytes and perfused liver of starved chickens showed that gluconeogenesis from lactate, glycerol and fructose was inhibited by 22-100% on addition of urate precursors. 2. The inhibition was associated with an increased rate of urate formation. 3. 2,4-Dinitrophenol (40 microM), 2-bromooctanoate (2 mM) and 3-mercaptopicolinate (3MPA) (0.5 mM) were inhibitory with respect to gluconeogenesis but did not significantly affect the rate of urate formation. 4. The possible interrelationships between gluconeogenesis and uricogenesis are considered in terms of a competition for ATP and for other metabolites between the two pathways. 5. An interplay of both pathways at the level of anion transfer across the inner mitochondrial membrane is also discussed.

The disposition of citric acid cycle intermediates by isolated rat heart mitochondria.

The mechanism of depletion of tricarboxylic acid cycle intermediates by isolated rat heart mitochondria was studied using hydroxymalonate (an inhibitor of malic enzymes) and mercaptopicolinate (an inhibitor of phosphoenolpyruvate carboxykinase) as tools. Hydroxymalonate inhibited the respiration rate of isolated mitochondria in state 3 by 40% when 2 mM malate was the only external substrate, but no inhibition was found with 2 mM malate plus 0.5 mM pyruvate as substrates. In the presence of bicarbonate, arsenite and ATP propionate was converted to pyruvate and malate at the rates of 14.0 +/- 2.9 and 2.8 +/- 1.8 nmol/mg protein in 5 min, respectively. Under these conditions, 0.1 mM mercaptopicolinate did not affect this conversion, but 2 mM hydroxymalonate inhibited pyruvate formation completely and resulted in an accumulation of malate up to 13.2 +/- 2.9 nmol/mg protein. No accumulation of phosphenolpyruvate was found under any condition tested. It is concluded that malic enzymes but not phosphoenolpyruvate carboxykinase, are involved in conversion of propionate to pyruvate in isolated rat heart mitochondria.

Phosphoenolpyruvate synthesis by fetal guinea-pig liver mitochondria.

Liver mitochondria isolated from fetal and newborn guinea pigs synthesized phosphoenolpyruvate at 4-6 nmol/min per mg protein with 2 mM malate, succinate, and alpha-ketoglutarate as substrates. These rates were 90-110% of that by adult liver mitochondria and were not substantially altered in the second half of gestation or within 24 h after birth. Both palmitoyl- and octanoylcarnitine were inhibitory to phosphoenolpyruvate synthesis in adult and fetal preparations, but free octanoate was inhibitory only in adult liver mitochondria.

[Redox state of free nicotinamide coenzymes and phosphoenolpyruvate synthesis in rat and guinea pig liver]. / Okislitel'no-vosstanovitel'noe sostoianie svobodnykh nikotinamidnykh kofermentov i sintez fosfoenolpiruvata v pecheni krys i morskikh svinok.

The paper deals with the redox state of free nicotinamide adenine dinucleotides (the NAD+/NADH ratio) in main compartments of the rat and guinea pig liver cells. NAD-pairs of cytoplasm and mitochondria in guinea pigs liver are shown to be more reduced than those in rats' liver. Stimulation of glucogenesis decreases the NAD+/NADH ratio in both compartments of rat liver and increases it in the guinea pigs' liver mitochondria. The guinea pigs' liver mitochondria synthesize actively phosphoenol pyruvate from oxaloacetate, malate and alpha-ketoglutarate. A decrease in the NAD+/NADH ratio value with introduction of beta-oxybutyrate into the incubation medium inhibits the phosphenolpyruvate synthesis from malate by 73%.

Fructose metabolism in four Pseudomonas species.

1. ATP-Dependent phosphorylation of fructose could not be detected in extracts of fructose-grown cells of Pseudomonas extorquens strain 16, Pseudomonas 3A2, Pseudomonas acidovorans and Pseudomonas fluorescens. Instead, phosphorylation of fructose to fructose-1-phosphate was found to occur when cell-free extracts were incubated with fructose and phosphoenolpyruvate. Such an activity could not be detected in cell-free extracts of succinate-grown cells. 2. High levels of 1-phosphofructokinase were found in extracts of the above organisms when growth on fructose. 3. Mutants of Pseudomonas extorquens strain 16 lacking 1-phosphofructokinase were unable to grow on fructose. Revertants to growth on fructose had regained the capacity to synthesize this enzyme, indicating its necessary involvement in fructose metabolism. 4. A survey has been carried out of enzymes involved in carbohydrate metabolism in the species listed above.

Unidirectional inhibition of phosphoenolpyruvate carboxykinase from Rhodospirillum rubrum by ATP.

The kinetic and regulatory properties of partially purified phosphoenolpyruvate (PEP) carboxykinase (EC 4.1.1.3.2) from Rhodospirillum rubrum were studied. The enzyme was active with guanosine- and inosinephosphates and must thus be classified as GTP (ITP): oxaloacetate carboxylase (transphosphorylating.) In the direction of oxaloacetate-foramtion, the enzyme was strongly inhibited by ATP (Ki = 0.03 mM). ITP, UTP, CTP, and GTP were less inhibitory. The inhibition was competitive with respect to GDP or IDP, but not with respect to PEP. In the direction of PEP-synthesis, the enzyme was not inhibited, but rather activated by ATP.

Phenethylbiguanide and the inhibition of hepatic gluconeogenesis in the guinea pig.

1. Phenethylbiguanide inhibits the synthesis of phosphoenolpyruvate from malate or 2-oxoglutarate by isolated guinea-pig liver mitochondria. This inhibition is time- and concentration-dependent, with the maximum decrease in the rate of phosphoenolpyruvate synthesis (80%) evident after 10min of incubation with 1mm-phenethylbiguanide. 2. The phosphorylation of ADP by these mitochondria is also inhibited at increasing concentrations of phenethylbiguanide and there is a progressive increase in AMP formation. Guinea-pig liver mitochondria are more sensitive to this inhibition in oxidative phosphorylation caused by phenethylbiguanide than are rat liver mitochondria. 3. Simultaneous measurements of O(2) consumption and ADP phosphorylation with guinea-pig liver mitochondria oxidizing malate plus glutamate in State 3 indicated that phenethylbiguanide at low concentrations (0.1mm) inhibits respiration at Site 1. At higher phenethylbiguanide concentrations Site 2 is also inhibited. 4. Gluconeogenesis from lactate, pyruvate, alanine and glycerol by isolated perfused guinea-pig liver is inhibited to various degrees by phenethylbiguanide. Alanine is the most sensitive to inhibition (60% inhibition of the maximum rate by 0.1mm-phenethylbiguanide), whereas glycerol is relatively insensitive (25% inhibition at 4mm). 5. Gluconeogenesis from lactate and pyruvate by perfused rat liver was also inhibited by phenethylbiguanide, but only at high concentrations (8mm). Unlike guinea-pig liver, the inhibitory effect of phenethylbiguanide on rat liver was reversible after the termination of phenethylbiguanide infusion. 6. The time-course of inhibition of gluconeogenesis from the various substrates used in this study indicated a time-dependency which was related in part to the concentration of infused phenethylbiguanidine. This time-course closely paralleled that noted for the inhibition by phenethylbiguanide of phosphoenolpyruvate synthesis in isolated guinea-pig liver mitochondria.