Diphosphate Moiety Research Articles

Homology of Escherichia coli B Glutathione Synthetase with Dihydrofolate Reductase in Amino Acid Sequence and Substrate Binding Site

Glutathione synthetase from Escherichia coli B showed amino acid sequence homology with mammalian and bacterial dihydrofolate reductases over 40 residues, although these two enzymes are different in their reaction mechanisms and ligand requirements. The effects of ligands of dihydrofolate reductase on the reaction of E. coli B glutathione synthetase were examined to find resemblances in catalytic function to dihydrofolate reductase. The E. coli B enzyme was potently inhibited by 7,8-dihydrofolate, methotrexate, and trimethoprim. Methotrexate was studied in detail and proved to bind to an ATP binding site of the E. coli B enzyme with K1 value of 0.1 mM. The homologous portion of the amino acid sequence in dihydrofolate reductases, which corresponds to the portion coded by exon 3 of mammalian dihydrofolate reductase genes, provided a binding site of the adenosine diphosphate moiety of NADPH in the crystal structure of dihydrofolate reductase. These analyses would indicate that the homologous portion of the amino acid sequence of the E. coli B enzyme provides the ATP binding site. This report gives experimental evidence that amino acid sequences related by sequence homology conserve functional similarity even in enzymes which differ in their catalytic mechanisms.

Two functional domains of coenzyme A activate catalysis by coenzyme A transferase. Pantetheine and adenosine 3‘-phosphate 5‘-diphosphate.

Studies of the reactivity of succinyl-CoA:3-keto acid CoA transferase with a small coenzyme A analog, methylmercaptopropionate, have shown that noncovalent interactions between the enzyme and the side chain of CoA are responsible for a rate acceleration of approximately 10(12), which is close to the total rate acceleration brought about by the enzyme (Moore, S. A., and Jencks, W. P. (1982) J. Biol. Chem. 257, 10893-10907). We report here that interaction between the enzyme and the pantetheine moiety of CoA provides the majority of the rate acceleration and destabilization of the enzyme-thiol ester intermediate that is observed with CoA substrates. The role of the adenosine 3'-phosphate 5'-diphosphate moiety of CoA is to provide 6.9 kcal/mol of binding energy in order to pull the pantetheine moiety into the active site. The enzyme-thiol ester intermediate, E-pantetheine, was generated by reaction of pantetheine with the thiol ester of enzyme and methylmercaptopropionate. E-Pantetheine undergoes hydrolysis with khyd = 2 min-1, 140-fold faster than E-CoA, and reacts with acetoacetate with kAcAc = 3 X 10(6) M-1 min-1, only 10-fold slower than E-CoA. However, in the reverse direction acetoacetylpantetheine reacts with CoA transferase (kAcAc-SP = 220 M-1 min-1) 1.6 X 10(6) times slower than acetoacetyl-CoA. The equilibrium constant for the reaction of pantetheine with E-CoA is approximately 8 X 10(-6).

Activation of 2-5A-dependent RNase by analogs of 2-5A (5'-O-triphosphoryladenylyl(2'—-5')adenylyl(2'—-5')adenosine ) using 2',5'-tetraadenylate (core)-cellulose.

A variety of 2-5A (px(A2'p)nA; x = 2 or 3, n greater than or equal to 2) analogs were assayed for their abilities to activate murine 2-5A-dependent RNase (subsequently "the nuclease") using a recently developed method. This technique consists of immobilizing and partially purifying the nuclease using core-cellulose [A2'p)3A-cellulose) and then monitoring the breakdown of poly(U)-3'-[32P]Cp into acid-soluble fragments. Several 5'-adenosinecapped analogs of 2-5A (containing a tetra-, tri-, or diphosphate) were analyzed, and it was found that reducing the number of phosphoryl groups between the 5' to 5'-diadenosine linkages resulted in a progressive loss of activity. Because A5' pppp(A2'p)3A was a potent activator of the nuclease yet stable during the assay these results suggested that a free 5'-phosphoryl group may not be required for the activation of the nuclease. A number of 8-bromoadenosine-substituted analogs of 2-5A were also studied. Curiously, the brominations decreased the activities of the 5'-di- and triphosphorylated molecules while substantially increasing the activities of the 5'-monophosphorylated species. The results indicated that a tri- or diphosphate moiety on the 5'-end of 2-5A or the presence of ATP is not absolutely required for the nuclease to be active. Furthermore, the ATP analog, beta, gamma-methylene ATP, did not inhibit the activity of the nuclease. Finally, a 3',5'-phosphodiester linkage isomer of 2-5A and a 3'-deoxy (cordycepin) analog of 2-5A were tested, and both were found to be completely without activity.

Structure and metal-binding properties of lipopolysaccharides from heptoseless mutants of Escherichia coli studied by 13C and 31P nuclear magnetic resonance.

The structure and metal-binding properties of lipopolysaccharides (LPS) from heptoseless mutants of Escherichia coli were studied by 13C and 31P NMR techniques. Carbon-13 NMR spectra were used to determine the linkages and configurations of the saccharide backbone and the types and locations of fatty acyl groups in E. coli LPS. Resonance assignments for native LPS were made by chemical shift correlation with model compounds, deacylated LPS, lipid A, deacylated lipid A, and fatty acids released from LPS by mild alkaline hydrolysis. The 3-deoxy-D-manno-octulosonate (KDO) disaccharide was tentatively assigned the structure KDO alpha 2 leads to 5KDO alpha 2 leads to. The presence of amide- and ester-linked 3-hydroxy and 3-acyloxy fatty acids in native LPS was confirmed directly from the 13C spectrum and evidence is presented for a labile acyl ester at C-3' (GlcNII) of the lipid A moiety. A significant finding was that the KDO disaccharide is linked to the C-6' position of the lipid A moiety, rather than C-3', as previously reported. The effects of binding Ca2+, Cd2+, Yb3+, Gd3+, and La3+ on the 31P NMR spectrum of LPS indicated that the glycosidic diphosphate moiety participates in a high affinity metal-binding site.

31P nuclear magnetic resonance study of phosphoribosyldiphosphate and its interaction with magnesium ions.

31P NMR has been used to study phosphoribosyldiphosphate (P-Rib-PP) over a wide range of pH values, both in the absence and presence of MgCl2. In the absence of MgCl2, the chemical shift variations of the three 31P nuclei in the molecule, over the pH range 4 to 9, were found to be largest for the terminal 1-diphosphate (1P beta) oxyanion and the 5-phosphate (5P) moiety. Apparent pK alpha values of approximately 6.1 and 6.3 were estimated for protonation of the 1P beta and 5P groups, respectively. Variations in the apparent pK alpha values associated with 1P beta and 5P oxyanions in the presence of various concentrations of MgCl2 were consistent with P-Rib-PP having two independent metal ion binding sites with different affinities for Mg2+ ions. The binding of Mg2+ reduced the apparent pK alpha of the 1P beta moiety by approximately 1.6 units and the apparent pK alpha of the 5P group by approximately 0.7 unit. This behavior is analogous to the situation reported for the terminal phosphooxyanion of ADP and observed for the phosphate group of ribose 5-phosphate, respectively. In the presence of an equimolar concentration of added MgCl2, the 1P alpha and 1P beta resonances of P-Rib-PP were shifted downfield and the 31P-31P coupling constant was decreased. Changes in both these parameters were very similar to those reported for the MgADP- complex. The observed chemical shifts and spin-spin coupling constants suggest that the diphosphate and monophosphate moieties of P-Rib-PP act as independent binding sites for Mg2+ in a manner similar to the phosphooxyanion groups of ADP and ribose 5-phosphate, respectively.

Mechanisms of the responses to non-cholinergic, non-adrenergic nerve stimulation and to ATP in isolated rabbit urinary bladder: evidence for ADP evoked prostaglandin release.

The contractile effects of ATP and related purine compounds on the isolated rabbit detrusor were investigated. It was found that ATP produced an initial rapid, phasic contraction followed by a slowly developing and maintained increase in tension. ADP caused a contraction closely mimicking the tonic response to ATP. The ADP induced contraction and the tonic response to ATP could both be abolished by indomethacin. beta, gamma-methylene ATP (APPCP), which is not degraded to ADP, elicited a rapid, phasic response, which could be abolished by nifedipine. AMP, dibutyryl-cAMP, and adenosine in low concentrations had no contractile effects; high concentrations of adenosine and 2-chloroadenosine, which is resistant to adenosine deaminase, decreased tone and spontaneous activity. The amplitude of the ATP induced contraction was positively correlated to the Ca2+-concentration in the extracellular medium; removal of Ca2+ abolished the ATP contraction before the responses to high K+ and carbachol disappeared. Responses to electrical field stimulation, mediated by non-cholinergic, non-adrenergic mechanisms were abolished by nifedipine and significantly reduced by indomethacin. It is concluded that in isolated rabbit detrusor, a direct contractile response can be elicited only by tripolyphosphates (ATP and APPCP), and that the diphosphate moiety ADP stimulates synthesis of prostaglandins The similarity between the effects of stimulation of non-cholinergic, non-adrenergic neurones and the phasic response to ATP supports the view that in rabbit detrusor ATP may be involved in excitation.

Identification of an NADH-linked disulfide reductase from Bacillus megaterium specific for disulfides containing pantethine 4',4“-diphosphate moieties.

Bacillus megaterium contains an NADH-linked disulfide reductase that is specific for disulfides containing pantethine 4',4''-diphosphate moieties. This reductase is at its highest level in cells late in sporulation and in dormant spores, and could be involved in the formation and cleavage of coenzyme A-protein disulfides which take place late in sporulation and early in spore germination, respectively.

Translation of Enzymically Decapped Messenger RNA

An enzymic procedure was used to remove the 7-methylguanosine diphosphate moiety at the 5' ends of rabbit hemoglobin mRNA and mouse immunoglobulin light-chain mRNA. Evidence was obtained that the procedure, which involves the use of polynucleotide kinase, does not result in any further degradation of the mRNA. The enzymically decapped mRNA was as effective as untreated mRNA in supporting protein synthesis in a wheat germ system. This was the case over a wide range of mRNA concentrations and over a considerable period of time. The presence in the incubation mixture of S-adenosylhomocysteine, an inhibitor of methylation, did not affect the results. The data indicate that the presence of a 7-methylguanosine diphosphate residue at the 5' end of mRNAs is not an obligatory requirement for translation in eucaryotic systems.

Choline sulfokinase of penicillium chrysogenum: Partial purification and kinetic mechanism

Choline sulfokinase (3′-phosphoadenosine 5′-phosphosulfate (PAPS):choline sulfotransferase, EC 2.8.2.6) was purified approximately 30-fold from the mycelium of Penicillium chrysogenum. The K m for PAPS is 12 μ m. The enzyme is remarkably specific for the adenosine 3′,5′ (or 2′-5′)-diphosphate moiety. 3′,5′-ADP (PAP) has a K i of 2.5 to 14 μ m (depending on the choline concentration) whereas the K i values of 3′-AMP, 5′-AMP, and 5′-ADP are at least 300-fold higher. The enzyme is also highly specific for choline ( K m = 17 μM). Of a number of other amino alcohols tested, none were potent inhibitors and only dimethylaminoethanol served as a reasonably good substrate ( K m = 800 μm V = 35% of V with choline). Triethylaminoethanol was a significantly poorer substrate ( K m = 2800 μM; V = 2% of V with choline). The purified enzyme is relatively stable when stored frozen in the presence of 25% sucrose. In the absence of sucrose, the maximum activity decreases and the K m for choline increases. (The K m for PAPS remains constant.) The age-inactivated enzyme can be restored to full activity (original V and K m for choline) by a 10-min preincubation with 50 m m mercaptoethanol. However, prolonged incubation (24 h) with 50 m m mercaptoethanol results in irreversible denaturation. Initial velocity studies established that the enzyme follows a sequential kinetic mechanism. Product inhibition studies suggest a rapid equilibrium random binding sequence. Choline- O-phosphate (a dead-end inhibitor) is linearly competitive with choline and a linear mixed type inhibitor with respect to PAPS. Choline analogs lacking the alcohol (or ester) group (e.g., trimethylammonium, neurine, chlorocholine) are competitive dead-end inhibitors with respect to choline but are uncompetitive with respect to PAPS. Thiocholine is a linear mixed type inhibitor with respect to PAPS, but the reciprocal plots are almost parallel. These results suggest that the analogs lacking an oxygen atom have a negligible affinity for the free enzyme and bind predominantly to the enzyme-PAPS complex.

Soluble Uridine Diphosphate d-Galactose:d-Glucose β-4-d-Galactosyltransferase from Bovine Milk

Abstract Some of the properties of a 70-fold purified bovine milk lactose synthetase have been determined. The enzyme preparation appears to be specific for uracil nucleoside diphosphate d-galactose derivatives. Adenosine, thymidine, cytidine, or guanosine diphosphate derivatives cannot serve as galactosyl donors for d-glucose to form lactose. The enzyme preparation will not transfer the galactosyl residue from uridine diphosphate d-galactose to α-d-glucose 1-phosphate, α-d-galactose 1-phosphate, d-xylose, maltose, α-methyl-d-glucoside, or l-glucose. N-Acetyl-d-glucosamine can serve as an acceptor for d-galactose but is only 25% as effective as d-glucose; the product of this reaction appears to be an analogue of lactose in which N-acetyl-d-glucosamine is substituted for d-glucose. It is not known whether these galactosyl transfer reactions are catalyzed by the same or a different enzyme. No reversal of the enzymatic reaction could be shown when lactose and UDP were used as substrates. The bovine milk lactose synthetase is activated by several divalent cations. The enzyme shows a maximum activation by Mn++, and an inhibition by ethylenediaminetetraacetate or Hg++. The enzyme has a 42° temperature optimum, and a pH optimum of 7.5, with maximum activity in sodium cacodylate-HCl or β,β'-dimethylglutarate-NaOH buffer. Phosphorylated compounds structurally related to the nucleoside diphosphate moiety of UDP-d-galactose strongly inhibit the enzymatic reaction whereas neutral hexoses or hexose phosphates produce little or no inhibition. The Km for UDP-d-galactose is 5.0 x 10-4 m, and that for d-glucose is 2.5 x 10-2 m.