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1.
Appropriate combinations of purified components of the reversible glycine cleavage system of rat liver catalyze three partial reactions: (1) decarboxylation of glycine or its reverse reaction catalyzed by P- and H-protein, (2) condensation of one carbon substrate and ammonia or its reverse reaction catalyzed by T- and H-protein, and (3) oxidation and reduction of active disulfide of H-protein catalyzed by L-protein. Reactions (1) and (2) give the same product which is bound to H-protein. The protein-bound product was isolated by gel filtration and converted to glycine by incubation with P-protein and CO2 or degraded further to one carbon unit and ammonia by incubation with T-protein and tetrahydrofolate. The data are consistent with the conclusion that the enzyme-bound product is an intermediate in the reversible glycine cleavage reaction. A scheme is presented for the reactions catalyzed by the enzyme system. 相似文献
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M Neuburger A M Polidori E Piètre M Faure A Jourdain J Bourguignon B Pucci R Douce 《European journal of biochemistry》2000,267(10):2882-2889
Lipoamide dehydrogenase or dihydrolipoamide dehydrogenase (EC 1.8.1. 4) is the E3-protein component of the mitochondrial 2-oxoacid dehydrogenase multienzyme complexes. It is also the L-protein component of the glycine decarboxylase system. Although the enzymology of this enzyme has been studied exhaustively using free lipoamide as substrate, no data are available concerning the kinetic parameters of this enzyme with its physiological substrates, the dihydrolipoyl domain of the E2 component (dihydrolipoyl acyltransferase) of the 2-oxoacid dehydrogenase multienzyme complexes or the dihydrolipoyl H-protein of the mitochondrial glycine decarboxylase. In this paper, we demonstrate that Tris(2-carboxyethyl)phosphine, a specific disulfide reducing agent, allows a continuous reduction of the lipoyl group associated with the H-protein during the course of the reaction catalysed by the L-protein. This provided a valuable new tool with which to study the catalytic properties of the lipoamide dehydrogenase. The L-protein displayed a much higher affinity for the dihydrolipoyl H-protein than for free dihydrolipoamide. The oxidation of the dihydrolipoyl H-protein was not affected by the presence of structurally related analogues (apoH-protein or octanoylated H-protein). In marked contrast, these analogues strongly and competitively inhibited the decarboxylation of the glycine molecule catalysed by the P-protein component of the glycine decarboxylase system. Small unfolded proteolytic fragments of the H-protein, containing the lipoamide moiety, displayed Km values for the L-protein close to that found for the H-protein. On the other hand, these fragments were not able to promote the decarboxylation of the glycine in the presence of the P-protein. New highly hydrophilic lipoate analogues were synthesized. All of them showed Km and kcat/Km values very close to that found for the H-protein. From our results we concluded that no structural interaction is required for the L-protein to catalyse the oxidation of the dihydrolipoyl H-protein. We discuss the possibility that one function of the H-protein is to maintain a high concentration of the hydrophobic lipoate molecules in a nonmicellar state which would be accessible to the catalytic site of the lipoamide dehydrogenase. 相似文献
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The exchange of glycine carboxyl carbon with CO2 catalyzed by the combination of chicken liver glycine decarboxylase (P-protein) and aminomethyl carrier protein (H-protein) was markedly inhibited by various divalent cations, although extents of inhibition by individual metal ions varied considerably. Cu2+ and Zn2+, at 100 microM, inhibited the reaction almost completely, and the inhibitions by Co2+ and Ni2+ were also significant, while Mg2+ and Mn2+ did not appreciably affect the reaction. The inhibition by Zn2+ was competitive with both bicarbonate and H-protein and non-competitive with glycine. Of the two reactions involved in the glycine-CO2 exchange, decarboxylation of glycine yielding the H-protein-bound aminomethyl moiety was not significantly affected by 100 microM Zn2+ or Cu2+, but carboxylation of the H-protein-bound aminomethyl moiety to form glycine was strongly inhibited by either Zn2+ or Cu2+. Various degrees of inhibition of the glycine-CO2 exchange by other divalent metal ions could also be accounted for by the inhibition of the carboxylation step of the exchange reaction. The primary site of the action of divalent metal ions is likely to be not P-protein but H-protein, and the binding of metal ions with the H-protein-bound intermediate of glycine decarboxylation was assumed to account for the observed marked inhibition. 相似文献
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A cytotoxic product of lipid peroxidation, 4-hydroxy-2-nonenal (HNE), rapidly inhibited glycine, malate/pyruvate, and 2-oxoglutarate-dependent O2 consumption by pea leaf mitochondria. Dose- and time-dependence of inhibition showed that glycine oxidation was the most severely affected with a K(0.5) of 30 microm. Several mitochondrial proteins containing lipoic acid moieties differentially lost their reactivity to a lipoic acid antibody following HNE treatment. The most dramatic loss of antigenicity was seen with the 17-kDa glycine decarboxylase complex (GDC) H-protein, which was correlated with the loss of glycine-dependent O2 consumption. Paraquat treatment of pea seedlings induced lipid peroxidation, which resulted in the rapid loss of glycine-dependent respiration and loss of H-protein reactivity with lipoic acid antibodies. Pea plants exposed to chilling and water deficit responded similarly. In contrast, the damage to other lipoic acid-containing mitochondrial enzymes was minor under these conditions. The implication of the acute sensitivity of glycine decarboxylase complex H-protein to lipid peroxidation products is discussed in the context of photorespiration and potential repair mechanisms in plant mitochondria. 相似文献
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Summary The glycine cleavage enzyme system is composed of four different proteins tentatively called P-protein, H-protein, T-protein and L-protein, and catalyzes the following reaction reversibly: Glycine + tetrahydrofolate + NAD+ 5, 10-methylene-tetrahydrofolate + NH3 + CO2 + NADH + H–
Glycine decarboxylase, tentatively called P-protein, is able by itself to catalyze glycine decarboxylation, yielding methylamine as product, but at an extremely low rate. P-Protein alone is also able to catalyze slightly the exchange of carboxyl carbon of glycine with CO2. However, the rates of the P-protein-catalyzed reactions are greatly increased by the co-existence of aminomethyl carrier protein, a lipoic acid-containing enzyme tentatively called H-protein. Several lines of evidence suggest that H-protein brings about a conformational change of P-protein which may be relevant to the expression of the decarboxylase activity of P-protein and that the functional glycine decarboxylase may be an enzyme complex composed of both P-protein and H-protein. H-Protein seems to play a dual role in the glycine decarboxylation; the one as a regulatory protein of P-protein, and the other as an electron-pulling agent and concomitantly as a carrier of the aminomethyl moiety derived from glycine. The idea that H-protein functions as a modulator of P-protein was further supported by the study of a patient with nonketotic hyperglycinemia. The primary lesion in this patient appeared to consist in structural abnormality in H-protein; the H-protein purified from the liver of this patient was apparently devoid of functional lipoic acid. Nevertheless, H-protein from the patient could stimulate the P-protein-catalyzed exchange of the carboxyl carbon of glycine and CO2, although only to a limited extent. The observed activity should be independent of the functioning of lipoic acid and would be a reflection of a conformational change in P-protein brought about by H-protein.P-Protein was inactivated when it was incubated with glycine in the presence of II-protein, and the inactivation was completely prevented when bicarbonate was further added so as to allow the glycine-CO2 exchange to proceed. The inactivation was accompanied by a spectral change of P-protein. The inactivation of P-protein seemed to take place as a side reaction of the glycine decarboxylation and to reflect the formation of a ternary complex of P-protein, H-protein and aminomethyl moiety of glycine through a Schiff base linkage of the H-protein-bound aminomethyl moiety with the pyridoxal phosphate of P-protein. 相似文献
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The glycine cleavage system catalyzes the oxidative decarboxylation of glycine in bacteria and in mitochondria of animals and plants. Its deficiency in human causes nonketotic hyperglycinemia, an inborn error of glycine metabolism. T-protein, one of the four components of the glycine cleavage system,is a tetrahydrofolate dependent aminomethyltransferase. It catalyzes the transfer of the methylene carbon unit to tetrahydrofolate from the methylamine group covalently attached to the lipoamide arm of H-protein. To gain insight into the T-protein function at the molecular level, we have determined the first crystal structure of T-protein from Thermotoga maritima by the multiwavelength anomalous diffraction method of x-ray crystallography and refined four structures: the apoform; the tetrahydrofolate complex; the folinic acid complex; and the lipoic acid complex. The overall fold of T-protein is similar to that of the C-terminal tetrahydrofolate-binding region (residues 421-830) of Arthrobacter globiformis dimethylglycine oxidase. Tetrahydrofolate (or folinic acid) is bound near the center of the tripartite T-protein. Lipoic acid is bound adjacent to the tetrahydrofolate binding pocket, thus defining the interaction surface for H-protein binding. A homology model of the human T-protein provides the structural framework for understanding the molecular mechanisms underlying the development of nonketotic hyperglycinemia due to missense mutations of the human T-protein. 相似文献
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The multi-enzyme complex glycine decarboxylase is important for one-carbon metabolism, essential for the photorespiratory glycolate cycle of plants, and comprises four different polypeptides, P-, H-, T-, and L-protein. We report on the production and properties of recombinant P-protein from the cyanobacterium Synechocystis and also describe features of recombinant H-protein from the same organism. The P-protein shows enzymatic activity with lipoylated H-protein and very low activity with H-apoprotein or lipoate as artificial cofactors. Its affinity towards glycine is unaffected by the presence and nature of the methyleneamine acceptor molecule. The cyanobacterial H-protein apparently forms stable dimers. 相似文献
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Cloning of cDNA encoding human H-protein, a constituent of the glycine cleavage system 总被引:1,自引:0,他引:1
K Hiraga S Kure M Yamamoto Y Ishiguro T Suzuki 《Biochemical and biophysical research communications》1988,151(2):758-762
A cDNA that encodes human H-protein, a constituent protein of the glycine cleavage system, was cloned with anti-rat H-protein antibody as a probe from a human liver cDNA library constructed with an expression vector, lambda gt11. The longest size of cDNA of the isolated clones was about 750 base long (lambda HH15B9). On the other hand, we determined the primary structure of human H-protein from the amino terminal Ser by the 12th Val, including a hexapeptide, -Glu-Lys-His-Glu-Trp-Val-. In addition to the finding that most cDNA inserts cloned hybridized with the synthetic DNA probe composed of the possible sequences for the hexapeptide, we confirmed that lambda HH15B9 encodes the partial primary structure of H-protein in an open reading frame. 相似文献
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Effects of the metabolites of the branched-chain amino acids and cysteamine on the glycine cleavage system 总被引:2,自引:0,他引:2
The effects of ten metabolites of the branched-chain amino acids, CoA and cysteamine (beta-mercaptoethylamine), on the glycine cleavage system were investigated with the liver extracts. It was found that CoA derivatives including tiglyl CoA, isobutyryl CoA, succinyl CoA, methylmalonyl CoA, isovaleryl CoA, propionyl CoA and CoA itself and cysteamine significantly inhibited the glycine cleavage system of the liver extracts. Further studies on the glycine-14CO2 exchange catalyzed by p-protein and H-protein purified from chicken liver indicated that tiglyl CoA inhibited the activity of P-protein in an apparently competitive manner with respect to H-protein, and that cysteamine inhibited the activity of P-protein in two ways, by increasing the Km value for glycine and changing Vmax. 相似文献
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The primary structure of human H-protein of the glycine cleavage system deduced by cDNA cloning 总被引:2,自引:0,他引:2
K Fujiwara K Okamura-Ikeda K Hayasaka Y Motokawa 《Biochemical and biophysical research communications》1991,176(2):711-716
A full-length cDNA encoding the human H-protein of the glycine cleavage system has been isolated from a lambda gt11 human fetal liver cDNA library. The cDNA insert was 1091 base pairs with an open reading frame of 519 base pairs which encoded a 125-amino acid mature human H-protein with a 48-amino acid presequence. Human H-protein is 97%, 86%, and 46% identical to the bovine, chicken, and pea H-protein, respectively. 相似文献
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Hydrogen carrier protein (H-protein), a component of the glycine cleavage system, has been purified to homogeneity from chicken liver mitochondria. The molecular weight and the partial specific volume determined by two different methods were 14,500 and 0.724 ml/g, respectively. The protein has an isoelectric point of 4.0. Amino acid analysis revealed 131 residues, about one-third of which are acidic residues. Evidence is presented indicating that the protein contains one lipoic acid moiety per molecule. In the decarboxylation of glycine the disulfide of the lipoyl moiety is cleaved and one of the resultant sulf-hydryl groups receives an intermediate derived from glycine. 相似文献
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Kazuko Okamura-Ikeda Harumi Hosaka Nobuo Maita Kazuko Fujiwara Akiyasu C. Yoshizawa Atsushi Nakagawa Hisaaki Taniguchi 《The Journal of biological chemistry》2010,285(24):18684-18692
Aminomethyltransferase, a component of the glycine cleavage system termed T-protein, reversibly catalyzes the degradation of the aminomethyl moiety of glycine attached to the lipoate cofactor of H-protein, resulting in the production of ammonia, 5,10-methylenetetrahydrofolate, and dihydrolipoate-bearing H-protein in the presence of tetrahydrofolate. Several mutations in the human T-protein gene are known to cause nonketotic hyperglycinemia. Here, we report the crystal structure of Escherichia coli T-protein in complex with dihydrolipoate-bearing H-protein and 5-methyltetrahydrofolate, a complex mimicking the ternary complex in the reverse reaction. The structure of the complex shows a highly interacting intermolecular interface limited to a small area and the protein-bound dihydrolipoyllysine arm inserted into the active site cavity of the T-protein. Invariant Arg292 of the T-protein is essential for complex assembly. The structure also provides novel insights in understanding the disease-causing mutations, in addition to the disease-related impairment in the cofactor-enzyme interactions reported previously. Furthermore, structural and mutational analyses suggest that the reversible transfer of the methylene group between the lipoate and tetrahydrofolate should proceed through the electron relay-assisted iminium intermediate formation. 相似文献
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Guilhaudis L Simorre JP Blackledge M Marion D Gans P Neuburger M Douce R 《Biochemistry》2000,39(15):4259-4266
The lipoate containing H-protein plays a pivotal role in the catalytic cycle of the glycine decarboxylase complex (GDC), undergoing reducing methylamination, methylene transfer, and oxidation. The transfer of the CH(2) group is catalyzed by the T-protein, which forms a 1:1 complex with the methylamine-loaded H-protein (Hmet). The methylamine group is then deaminated and transferred to the tetrahydrofolate-polyglutamate (H(4)FGlu(n)) cofactor of T-protein, forming methylenetetrahydrofolate-polyglutamate. The methylamine group is buried inside the protein structure and highly stable. Experimental data show that the H(4)FGlu(n) alone does not induce transfer of the methylene group, and molecular modeling also indicates that the reaction cannot take place without significant structural perturbations of the H-protein. We have, therefore, investigated the effect of the presence of the T-protein on the stability of Hmet. Addition of T-protein without H(4)FGlu(n) greatly increases the rate of the unloading reaction of Hmet, reducing the activation energy by about 20 kcal mol(-1). Differences of the (1)H and (15)N chemical shifts of the H-protein in its isolated form and in the complex with the T-protein show that the interaction surface for the H-protein is localized on one side of the cleft where the lipoate arm is positioned. This suggests that the role of the T-protein is not only to locate the tetrahydrofolate cofactor in a position favorable for a nucleophilic attack on the methylene carbon but also to destabilize the H-protein in order to facilitate the unlocking of the arm and initiate the reaction. 相似文献
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Control of photosynthesis in barley plants with reduced activities of glycine decarboxylase 总被引:4,自引:0,他引:4
A mutant (LaPr 87/30) of barley (Hordeum vulgare L.) deficient in glycine decarboxylase (GDC; EC 2.1.2.10) was crossed with wild-type plants to generate heterozygous plants
with reduced GDC activities. Plants of the F2 generation were grown in air and analysed for reductions in GDC proteins and GDC activity. The leaves of heterozygous plants
contained reduced amounts of H-protein, and when the content of H-protein was lower than 60% of the wild-type, the P-protein
was also reduced. The contents of the other two proteins of the GDC complex, T-protein and L-protein were not affected. Glycine
decarboxylase activities, measured as the decarboxylation of [1-14C]glycine by intact mitochondria released from protoplasts, were between 47% and 63% of the wild-type activity in heterozygous
plants and between 86% and 100% in plants with normal contents of H-protein. The enzyme activity was linearly correlated with
the relative content of H-protein. Plants with reduced GDC activities developed normally and did not show major pleiotropic
effects. In air, the reduction in GDC activity had no effect on the leaf metabolite content or photosynthesis, but under conditions
of enhanced photorespiration (low CO2 and high light), glycine accumulated and the rates of photosynthesis decreased compared to the wild-type. The accumulation
of glycine did not lead to a depletion of amino donors or to the accumulation of glyoxylate. The lower rates of photosynthesis
were probably caused by an impaired recycling of carbon in the photorespiratory pathway. It is concluded that GDC has no control
over CO2 assimilation under normal growth conditions, but appreciable control by GDC becomes apparent under conditions leading to
higher rates of photorespiration.
Received: 24 November 1996 / Accepted: 23 January 1997 相似文献