The stimulation by phosphate and the inhibition by adenine nucleotides and nicotinamide–adenine dinucleotide of the respiratory chain

1968 ◽  
Vol 46 (4) ◽  
pp. 315-321 ◽  
Author(s):  
M. C Blanchaer
Keyword(s):  
Respiratory Chain ◽  
Electron Acceptor ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nadh Dehydrogenase ◽  
Adenine Nucleotides ◽  
Coenzyme Q ◽  
Steady State Kinetic ◽  
Competitive Inhibitors ◽  
Energy Conserving ◽  
State Kinetic

Steady-state kinetic experiments with pigeon heart mitochondria and electron-transport particles (ETPH), with NADH as substrate in the absence of phosphate and with coenzyme Q1 or ferricyanide as the electron acceptor showed that ADP and ATP are competitive inhibitors at the NADH dehydrogenase level of the respiratory chain. The ADP effect was hyperbolic competitive in type indicating that this nucleotide inhibits by decreasing the affinity of the dehydrogenase for NADH rather than by competing for the NADH binding site of the enzyme. The inhibition by ADP and ATP does not involve energy-conserving reactions since it is not relieved by oligomycin or Dicoumarol. NAD+ also is an inhibitor of the NADH dehydrogenase of ETPH but is noncompetitive with respect to NADH. Phosphate stimulates NADH oxidation by ETPH and mitochondria in the absence of ADP when O2 is the electron acceptor. Since this effect is absent when CoQ1 or ferricyanide replaces O2 as the acceptor, it would appear that phosphate stimulates the respiratory chain on the O2 side of ubiquinone during noncoupled respiration.

The inhibition of mammalian mitochondrial NADU oxidation by chloramphenicol and its isomers and analogues

1968 ◽  
Vol 46 (9) ◽  
pp. 1003-1008 ◽  
Author(s):  
K. B. Freeman ◽  
D. Haldar
Keyword(s):  
Cytochrome B ◽  
Respiratory Chain ◽  
Rat Liver ◽  
Nadh Dehydrogenase ◽  
Coenzyme Q ◽  
Liver Mitochondria ◽  
Heart Mitochondria ◽  
Rat Liver Mitochondria ◽  
Beef Heart ◽  
Beef Heart Mitochondria

Chloramphenicol and its isomers and analogues have been found to inhibit the oxidation of NADH, but not that of succinate, by beef heart mitochondria. They must therefore inhibit the NADH dehydrogenase segment of the respiratory chain. Chloramphenicol gave 50% inhibition at a concentration of 1 mM. The methylthio analogue of chloramphenicol inhibited NADH – coenzyme Q6 reductase but not NADH–ferricyanide reductase. Spectrophotometric observations suggest that these inhibitors act between NADH and flavin in coupled rat liver mitochondria and between flavin and cytochrome b in uncoupled beef heart mitochondria.

scholarly journals Proton-linked l-rhamnose transport, and its comparison with l-fucose transport in Enterobacteriaceae

1993 ◽  
Vol 290 (3) ◽  
pp. 833-842 ◽  
Author(s):  
J A R Muiry ◽  
T C Gunn ◽  
T P McDonald ◽  
S A Bradley ◽  
C G Tate ◽  
...  
Keyword(s):  
Transport System ◽  
Erwinia Carotovora ◽  
Alkaline Ph ◽  
Transport Activity ◽  
Ph Change ◽  
Kinetic Measurements ◽  
E Coli ◽  
Steady State Kinetic ◽  
Competitive Inhibitors ◽  
State Kinetic

1. An alkaline pH change occurred when L-rhamnose, L-mannose or L-lyxose was added to L-rhamnose-grown energy-depleted suspensions of strains of Escherichia coli. This is diagnostic of sugar-H+ symport activity. 2. L-Rhamnose, L-mannose and L-lyxose were inducers of the sugar-H+ symport and of L-[14C]rhamnose transport activity. L-Rhamnose also induced the biochemically and genetically distinct L-fucose-H+ symport activity in strains competent for L-rhamnose metabolism. 3. Steady-state kinetic measurements showed that L-mannose and L-lyxose were competitive inhibitors (alternative substrates) for the L-rhamnose transport system, and that L-galactose and D-arabinose were competitive inhibitors (alternative substrates) for the L-fucose transport system. Additional measurements with other sugars of related structure defined the different substrate specificities of the two transport systems. 4. The relative rates of H+ symport and of sugar metabolism, and the relative values of their kinetic parameters, suggested that the physiological role of the transport activity was primarily for utilization of L-rhamnose, not for L-mannose or L-lyxose. 5. L-Rhamnose transport into subcellular vesicles of E. coli was dependent on respiration, was optimal at pH 7, and was inhibited by protonophores and ionophores. It was insensitive to N-ethylmaleimide or cytochalasin B. 6. L-Rhamnose, L-mannose and L-lyxose each elicited an alkaline pH change when added to energy-depleted suspensions of L-rhamnose-grown Salmonella typhimurium LT2, Klebsiella pneumoniae, Klebsiella aerogenes, Erwinia carotovora carotovora and Erwinia carotovora atroseptica. The relative rates of subsequent acidification varied, depending on both the organism and the sugar. L-Fucose promoted an alkaline pH change in all the L-rhamnose-induced organisms except the Erwinia species. No L-rhamnose-H+ symport occurred in any organism grown on L-fucose. 7. All these results showed that L-rhamnose transport into the micro-organisms occurred by a system different from that for L-fucose transport. Both systems are energized by the trans-membrane electrochemical gradient of protons. 8. Neither steady-state kinetic measurements nor binding-protein assays revealed the existence of a second L-rhamnose transport system in E. coli.

scholarly journals Activity of fluoro and deoxy analogues of glycerol as substrates and inhibitors of glycerol kinase

1972 ◽  
Vol 130 (1) ◽  
pp. 199-205 ◽  
Author(s):  
Robert Eisenthal ◽  
Roger Harrison ◽  
William J. Lloyd ◽  
Norman F. Taylor
Keyword(s):  
Steady State ◽  
Hydroxy Group ◽  
Glycerol Kinase ◽  
Similar Activity ◽  
System A ◽  
Steady State Kinetic ◽  
Convenient Synthesis ◽  
Competitive Inhibitors ◽  
Hydroxy Groups ◽  
State Kinetic

Analogues of glycerol in which each of the three hydroxy groups is successively replaced by fluorine or hydrogen have been examined as substrates or inhibitors of glycerol kinase (Candida mycoderma) to assess the ability of fluorine to mimic a substrate hydroxy group in enzyme–analogue interactions. The four diols resulting from replacement of the hydroxy groups at C-1 or C-2 of sn-glycerol by fluorine or hydrogen are weak substrates. Similar substitution of the C-3 hydroxy group gives compounds which act as competitive inhibitors of glycerol or dihydroxyacetone phosphorylation but show no activity as substrates. Comparison of the steady-state kinetic parameters of the corresponding analogues shows that replacement of a hydroxy group by either fluorine or hydrogen leads to compounds with similar activity in this system. A convenient synthesis of (+)-propane-1,2-diol is described.

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