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PubMed1985

Effects of feed restriction on growth and metabolism of replacement pullets.

The effects of feed restriction on lipogenesis, carcass composition, and protein utilization were investigated. Two feed restriction programs were used: restricted duration of feeding (RDF) whereby pullets had access to feed for 7 or 9 hr/day and restricted access to feed (ADF) in which feed was available on alternate days. A control group received the same diet as the restricted groups but on an ad libitum basis. The feeding programs were applied to a white egg and brown egg strain of commercial laying hens from 1 until 5 weeks of age or from 3 days (RDF) or 10 weeks (ADF) until 19 weeks of age. The ADF restriction resulted in 12 to 25% decrease in body weights at 5 weeks and 5 to 11% decrease in body weights at 18 or 19 weeks. The RDF depressed body weights 24% at 5 weeks and 2% at 18 weeks. The RDF and ADF increased hepatic malic enzyme and glutamic oxaloacetic transaminase activities in both age groups. Plasma uric acid and hepatic glutamic pyruvic transaminase were affected, but not consistently, by ADF. It is hypothesized that ADF and RDF lead to increased lipogenesis and increased utilization of amino acids as sources of energy. Under conditions of mild restriction, this may result in increased carcass fat content.

Adipose Tissue↗
PubMed1984

Colchicine inhibition of insulin induction of stearoyl-CoA desaturase and fatty acid synthetase in cultured avian liver explants.

Chicken embryo liver explants cultured in chemically defined medium in the absence of serum provide a unique system to probe into the mechanism of insulin induction of lipogenic enzymes. Colchicine at concentrations of 0.2 and 1 microM in the culture medium caused inhibition of insulin induction of stearoyl-CoA desaturase and fatty acid synthetase by 50 and 90%, respectively. As measured by immunochemical techniques, the inhibition of the induction of these two enzyme systems resulted from the decreased content of the delta 9-terminal desaturase component of the stearoyl-CoA desaturase and the fatty acid synthetase. Colchicine, however, had no effect on the general protein synthesis, nor did it affect the malic enzyme, which is induced by triiodothyronine but not by insulin. Also, colchicine had no influence on the binding of 125I-insulin to isolated plasma membrane. Pretreatment of liver explants with insulin for 0.5-1 h and subsequent incubation in insulin-free media for 48 h resulted in induction of the desaturase and fatty acid synthetase. However, inclusion of colchicine in the media for 3 h subsequent to the treatment with insulin completely abolished the inductive effect of insulin, suggesting that colchicine affects events occurring subsequent to insulin binding to the cell surface membranes. Since lumicolchicine, an inactive isomer of colchicine, had no effect on insulin action, it is suggested that the inhibition of insulin induction of the desaturase and synthetase is related to the depolymerizing action of colchicine. Therefore, in eliciting long-term responses to insulin, microtubular integrity of the cell may be required for the transfer of a putative from cell surface insulin receptor to intracellular sites.

Animals↗
PubMed2004

Effect of five cysteine-containing compounds on three lipogenic enzymes in Balb/cA mice consuming a high saturated fat diet.

The in vivo effects of N-acetyl cysteine (NAC), S-allyl cysteine, S-ethyl cysteine (SEC), S-methyl cysteine (SMC), and S-propyl cysteine (SPC) against hyperlipidemia development and oxidation stress in Balb/cA mice consuming a high saturated fat diet were examined. The influence of these agents on plasma levels of glucose, insulin, uric acid, TG, cholesterol, and the activity of three lipogenic enzymes--glucose-6-phosphate dehydrogenase, malic enzyme, and FA synthase--was determined. All mice consumed the coconut oil-basd, high saturated fat diet, water, and cysteine or one of the five cysteine-containing compounds for 4 wk. The diet with 18% saturated fat significantly elevated the activity of three lipogenic enzymes and significantly increased TG and cholesterol biosynthesis in plasma and liver (P < 0.05). When compared with the water and cysteine groups, the treatments from five cysteine-containing agents significantly reduced high saturated fat diet-increased malic enzyme and FA synthase activities, and significantly lowered TG levels in plasma and liver (P< 0.05); however, only NAC, SAC, and SMC treatments significantly reduced cholesterol levels in plasma and liver (P < 0.05). The five cysteine-containing agents significantly restored high saturated fat diet-decreased glutathione peroxidase (GPX) activity in liver (P< 0.05); however, only SMC and SPC significantly restored GPX activity in heart and kidney (P< 0.05). These agents also significantly improved high saturated fat diet-related hyperglycemia, hyperuricemia, and oxidation stress (P < 0.05). These data support the hypothesis that these compounds are potential multiply-protective agents for hyperlipidemia prevention or therapy.

Acetylcysteine↗
PubMed1977

Mechanism of pigeon liver malic enzyme: kinetics, specificity, and half-site stoichiometry of the alkylation of a cysteinyl residue by the substrate-inhibitor bromopyruvate.

Malic enzyme from pigeon liver is alkylated by the substrate analogue bromopyruvate, resulting in the concomitant loss of its oxidative decarboxylase and oxalacetate decarboxylase activities, but not its ability to reduce alpha-keto acids. The inactivation of oxidative decarboxylase activity follows saturation kinetics, indicating the formation of an enzyme-bromopyruvate complex (K congruent to 8 mM) prior to alkylation. The inactivation is inhibited by metal ions and pyridine nucleotide cofactors. Protection of malic enzyme by the substrates L-malate and pyruvate and the inhibitors tartronate and oxalate requires the presence of the above cofactors, which tighten the binding of these carboxylic acids in accord with the ordered kinetic scheme (Hsu, R. Y., Lardy, H. A., and Cleland, W. W. (1967), J. Biol. Chem. 242, 5315-5322). Bromopyruvate is reduced to L-bromolactate by malic enzyme and is an effective inhibitor of L-malate and pyruvate in the overall reaction. The apparent kinetic constants (90 muM-0.8 mM) are one to two orders of magnitude lower than the half-saturation constant (K) of inactivation, indicating a similar tightening of bromopyruvate binding in the E-NADP+ (NADPH)-Mn2+ (Mg2+)-BP complexes. During alkylation, bromopyruvate interacts initially at the carboxylic acid substrate pocket of the active site, as indicated by the protective effect of substrates and the ability of this compound to form kinetically viable complexes with malic enzyme, particularly as a competitive inhibitor of pyruvate carboxylation with a Ki (90 muM) in the same order as its apparent Michaelis constant of 98 muM. Subsequent alkylation of a cysteinyl residue blocks the C-C bond cleavage step. The incorporation of radioactivity from [14C]bromopyruvate gives a half-site stoichiometry of two carboxyketomethyl residues per tetramer, indicating strong negative cooperativity between the four subunits of equal size, or alternatively the presence of structurally dissimilar active sites.

Affinity Labels↗
PubMed2006

Pharmacological doses of triiodothyronine upregulate lipogenic enzyme gene expression in rat white adipose tissue.

Triiodothyronine (T (3)) is known to increase liver lipogenic enzyme gene expression both in vivo and in tissue culture. Conflicting results have been reported on the effect of T (3) on lipogenic enzyme gene expression in white adipose tissue. The results presented in this paper indicate that administration of pharmacological doses of T (3) in rats leads to increased fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), ATP-citrate lyase (ACL) and malic enzyme (ME) activity in white adipose tissue. The increase in lipogenic enzyme activity was associated with increased FAS, ACC, ACL and ME mRNA levels. The response was dose-dependent. Activity of lipogenic enzyme and the lipogenic enzyme mRNA levels were positively correlated to serum T (3) concentration. The in vivo effect of T (3) on lipogenic enzyme gene expression could be reproduced in primary white rat adipocyte culture. In conclusion, the results presented in this paper indicate that T (3) exerts a stimulatory effect on lipogenic enzyme gene expression in white adipose tissue both in vivo and in tissue culture. Significant effects of T (3) on lipogenic enzyme gene expression were only observed in the presence of relatively high (pharmacological) concentrations of the hormone.

Adipocytes↗
PubMed1986

The Involvement of Aspartate and Glutamate in the Decarboxylation of Malate by Isolated Bundle Sheath Chloroplasts from Zea mays.

Aspartate or glutamate stimulated the rate of light-dependent malate decarboxylation by isolated Zea mays bundle sheath chloroplasts. Stimulation involved a decrease in the apparent K(m) (malate) and an increased maximum velocity of decarboxylation. In the presence of glutamate other dicarboxylates (succinate, fumarate) competitively inhibited malate decarboxylation by intact chloroplasts with respect to malate with an apparent K(i) of about 6 millimolar. For comparison the K(i) for inhibition of nicotinamide adenine dinucleotide phosphate-malic enzyme from freshly lysed chloroplasts by these dicarboxylates was 15 millimolar. A range of compounds structurally related to aspartate stimulated malate decarboxylation by intact chloroplasts. K(a) values for stimulation at 5 millimolar malate were 1.7, 5, and 10 millimolar for l-glutamate, l-aspartate, and beta-methyl-dl-aspartate, respectively. Certain compounds, notably cysteic acid, which stimulated malate decarboxylation by intact chloroplasts inhibited malate decarboxylation by nicotinamide adenine dinucleotide phosphate-malic enzyme obtained from lysed chloroplasts and assayed under comparable conditions. It was concluded that aspartate, glutamate, and related compounds affect the transport of malate into the intact chloroplasts and that malate translocation does not take place on the general dicarboxylate translocator previously reported for higher plant chloroplasts.

Journal Article↗
PubMed1963

DENATURATION AND RENATURATION OF MALIC DEHYDROGENASE IN A CELL-FREE EXTRACT FROM A MARINE PSYCHROPHILE.

Burton, Sheril D. (Oregon State University, Corvallis), and Richard Y. Morita. Denaturation and renaturation of malic dehydrogenase in a cell-free extract from a marine psychrophile. J. Bacteriol. 86:1019-1024. 1963.-Malic dehydrogenase from a marine psychrophilic vibrio (PS 207) was found to be heat-sensitive at 30 C, the maximal growth temperature for the organism. Initial denaturation was reversible, with maximal renaturation occurring when the denatured enzyme was slowly cooled in the presence of mercaptoethanol, reduced nicotinamide adenine dinucleotide, and malate. No renaturation occurred when these compounds were added after slow cooling, or when the renaturation mixture was rapidly cooled. Mercaptoethylamine, cysteine, glutathione, or mercaptoacetic acid could not replace mercaptoethanol. The kinetics of denaturation and renaturation suggest the presence of several malic isozymes each with different heat labilities, or that these processes are occurring in several distinct steps.

Bacteria↗
PubMed1995

Effects of acute exercise on hepatic lipogenic enzymes in fasted and refed rats.

The effects of an acute bout of prolonged exhaustive exercise on the activities of hepatic lipogenic enzymes have been investigated. Male Sprague-Dawley rats were randomly divided into three groups: fasted for 48 h without refeeding (FA) and fasted for 48 h and refed a diet high in fructose (RF) or in cornstarch (RC). One-half of each group of rats exercised on a treadmill at 20 m/min, 5% grade, until exhaustion and the other half rested for the same amount of time without food. Dietary intakes during refeeding were kept equal between the exercised and rested control animals. Activities of all hepatic lipogenic enzymes measured, i.e., fatty acid synthase (FAS), L-type pyruvate kinase (L-PK), ATP citrate lyase, malic enzyme, and glucose-6-phosphate dehydrogenase, were induced dramatically by fasting-refeeding and were significantly higher in the RF than in the RC rats (P < 0.05). FAS activity was increased 19- and 39-fold, respectively, in the RC and RF rats compared with the FA rats. Exercise decreased FAS activity to approximately one-third of the resting control value in both RC and RF rats (P < 0.05) but not in FA rats. L-PK activity was elevated by 55% in RC and 100% in RF rats compared with FA rats (P < 0.05). FA and RF rats also showed a reduction of L-PK activity with exercise. No significant alteration of other lipogenic enzymes was observed after exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP Citrate (pro-S)-Lyase↗
PubMed2004

Amino acid biosynthesis and metabolic flux profiling of Pichia pastoris.

Amino acid biosynthesis and central carbon metabolism of Pichia pastoris were studied using biosynthetically directed fractional (13)C labeling. Cells were grown aerobically in a chemostat culture fed at two dilution rates (0.05 h(-1), 0.16 h(-1)) with glycerol as the sole carbon source. For investigation of amino acid biosynthesis and comparison with glycerol cultivations, cells were also grown at 0.16 h(-1) on glucose. Our results show that, firstly, amino acids are synthesized as in Saccharomyces cerevisiae. Secondly, biosynthesis of mitochondrial pyruvate via the malic enzyme is not registered for any of the three cultivations. Thirdly, transfer of oxaloacetate across the mitochondrial membrane appears bidirectional, with a smaller fraction of cytosolic oxaloacetate stemming from the mitochondrial pool at the higher dilution rate of 0.16 h(-1) (for glucose or glycerol cultivation) when compared to the glycerol cultivation at 0.05 h(-1). Fourthly, the fraction of anaplerotic synthesis of oxaloacetate increases from 33% to 48% when increasing the dilution rate for glycerol supply, while 38% is detected when glucose is fed. Finally, the cultivation on glucose also allowed qualitative comparison with the flux ratio profile previously published for Pichia stipitis and S. cerevisiae grown on glucose in a chemostat culture at a dilution rate of 0.1 h(-1). This provided a first indication that regulation of central carbon metabolism in P. pastoris and S. cerevisiae might be more similar to each other than to P. stipitis.

Amino Acids↗
PubMed1977

Effect of prolonged ethanol ingestion on hepatic lipogenesis and related enzyme activities.

1. Hepatic lipogenesis in vivo and the activities of enzymes associated with fatty acid synthesis in the liver were studied in rats fed for 21 days on liquid diets containing ethanol. 2. The ethanol-fed rats developed a moderate hepatic triacylglycerol accumulation during this period. When carbohydrate was replaced by ethanol in the diet, the rate of fatty acid synthesis was slower in the ethanol-fed rats on low-, medium- and high-fat diets than in the appropriate controls. However, when the fat/carbohydrate ratio was kept the same in the ethanol-fed and control rats, ethanol had no influence on the rate of fatty acid synthesis. 3. Glucose 6-phosphate dehydrogenase activity was lower in the ethanol-fed group. ;Malic' enzyme activity did not change during the ethanol treatment when the fat/carbohydrate ratio was kept unchanged. 4. The ATP citrate lyase activity was lower in the ethanol-fed rats on all diets, whereas acetyl-CoA synthetase activity was independent of the composition of the control diet, but was lower in the ethanol-fed rats, in which the concentration of the active form of pyruvate dehydrogenase was also lower. 5. It is concluded that hepatic fatty acid synthesis does not play any major role in ethanol-induced triacylglycerol accumulation. Careful design of the diets is necessary to reveal the specific effects of ethanol on the enzymes associated with lipogenesis.

Acetate-CoA Ligase↗
PubMed1976

[Study of properties of NADP malate dehydrogenase from corn leaves].

Kinetic properties of purified chloroplast isoenzyme of the "malic" enzyme from corn leaves were studied. The enzyme had optimum activity at pH 8.0 and 36 degrees C. Under standart conditions the Michaelis constants for the "malic" enzyme with Mn2+ as cofactor are 0.091 mM for malate and 0.04 mM for NADP. In case of Mg2+ as cofactor they are 0.66 and 0.02 mM respectively. Respective Km values for the cofactors Mn2+ and Mg2+ are 0.018 and 0.091 mM. The activity of the "malic" enzyme was inhibited by reduced NADP and NAD, ATP, ADP, fructose-1,6-diphosphate, oxaloacetic, oxalic, glyoxylic, glycolic and alpha-ketoglutaric acids, as well as by phosphate anions and pyrophosphate. The inhibitory effect of all metabolites and ions is more pronounced in case of Mn, rather than Mg, used as cofactors for the reaction. A possibility of metabolic regulation of NADP-"malic" enzyme activity in the leaves of C4-plants, is discussed.

Adenosine Diphosphate↗
PubMedDate not supplied

Primary structure of the hydrogenosomal malic enzyme of Trichomonas vaginalis and its relationship to homologous enzymes.

The complete nucleotide sequence has been established for two genes (maeA and maeB) coding for different subunits of the hydrogenosomal malic enzyme [malate dehydrogenase (decarboxylating) EC 1.1.1.39] of Trichomonas vaginalis. Two further genes (maeC and maeD) of this enzyme have been partially sequenced. The complete open reading frames code for polypeptides of 567 amino acids in length. These two open reading frames are similar with less than 12 percent pairwise nucleotide differences and less than 9 percent pairwise amino acid differences. The open reading frames of the two partially sequenced genes correspond to the amino-terminal part of the polypeptides coded and are similar to the corresponding parts of the completely sequenced ones. The deduced translation products of the two complete genes differ in their calculated pI values by 1.5 pH unit. The genes code for polypeptides which contain 12 or 11 amino-terminal amino-acyl residues not present in the proteins isolated from the cell. Other hydrogenosomal enzymes also have similar amino-terminal extensions which probably play a role in organellar targeting and translocation of the newly synthesized polypeptides. A comparison of 19 related enzymes from bacteria and eukaryotes with the maeA product revealed 34-45 percent amino acid identity. Phylogenetic reconstruction based on nonconservative amino acid differences with maximum parsimony (phylogenetic analysis using parsimony, PAUP) and distance based (neighbor-joining, NJ) methods showed that the T. vaginalis enzyme is the most divergent of all eukaryotic malic enzymes, indicating its long independent evolutionary history.

Amino Acid Sequence↗
PubMed1987

Evidence for a multiple subunit composition of plant NAD malic enzyme.

Malate dehydrogenase (decarboxylating) (EC 1.1.1.39) was purified to near homogeneity from both a C3 plant, Solanum tuberosum, and a CAM plant, Crassula argentea. Sodium dodecyl sulfate-gel electrophoresis of both enzymes revealed an alpha,beta subunit composition with corresponding molecular mass assignments of 61,000 and 55,000 daltons. Isoelectric focusing under native conditions showed only one constituent malic enzyme form with an isoelectric point of 5.1. No evidence of additional isoenzymes was found. Urea isoelectric focusing showed the alpha subunit to be more acidic than the beta subunit. Peptide mapping by limited proteolysis with Staphylococcus aureus V-8 protease, trypsin, and endoproteinase Arg-C eliminated the possibility that a precursor-product relationship may have existed between the two subunits and demonstrated that they each possess unique primary sequences. Further support for this conclusion was obtained when significant differences in the contents of glutamic acid, isoleucine, and arginine were revealed by amino acid analysis of the isolated subunits. There was no apparent activity associated with the separated subunits (as resolved by urea-DEAE chromatography), but activity could be found in a reconstituted system, thereby indicating an (alpha,beta)n protomeric configuration. This is the first case where malic enzyme has been conclusively shown to be constructed from nonidentical subunits. This phenomenon has been observed only for the NAD malic enzyme isolated from plants.

Amino Acids↗
PubMed1984

Characterization of Early Morning Crassulacean Acid Metabolism in Opuntia erinacea var Columbiana (Griffiths) L. Benson.

The nature and sequence of metabolic events during phase II (early morning) Crassulacean acid metabolism in Opuntia erinacea var columbiana (Griffiths) L. Benson were characterized. Gas exchange measurements under 2 and 21% O(2) revealed increased O(2) inhibition of CO(2) fixation with progression of phase II. Malate and titratable acidity patterns indicated continued synthesis of C(4) acids for at least 30 minutes into the light period. Potential activities of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme exhibited little change during phase II, while light activation of NADP-malate dehydrogenase, pyruvate, orthophosphate dikinase, and ribulose-1,5-bisphosphate carboxylase was apparent. Short-term (14)CO(2) fixation experiments showed that the per cent of (14)C incorporated into C(4) acids decreased while incorporation into other metabolites increased with time. PEPC exhibited increased sensitivity to 2 millimolar malate, and the K(i)(malate) for PEPC decreased markedly with time. Sensitivity of PEPC to malate inhibition was considerably greater at pH 7.5 than at 8.0. The results indicate that decarboxylation and synthesis of malate occur simultaneously during the early morning period, and that phase II acid metabolism is not limited by CO(2) diffusion through stomata. With progression of phase II, CO(2) fixation by PEPC decreases while fixation by ribulose-1,5-bisphosphate carboxylase increases.

Journal Article↗