Effect of Early Iron Deficiency in Rat on the γ-Aminobutyric Acid Shunt in Brain

Early iron deficiency in rat does not affect the weight or the protein, DNA, and RNA content but results in a slight reduction in gamma-aminobutyric acid (GABA) (13%, p less than 0.01) and glutamic acid (20%, p less than 0.001) content of the brain. The activities of the two GABA shunt enzymes, glutamate dehydrogenase and GABA-transaminase, and of the NAD+-linked isocitrate dehydrogenase (ICDH) were inhibited whereas the glutamic acid decarboxylase, mitochondrial NADP+-linked ICDH, and succinic dehydrogenase activities remained unaltered in brain. On rehabilitation with the iron-supplemented diet for 1 week, these decreased enzyme activities in brain attained the corresponding control values. However, the hepatic nonheme iron content increased to about 80% of the control, after rehabilitation for 2 weeks. A prolonged iron deficiency resulting in decreased levels of glutamate and GABA may lead to endocrinological, neurological, and behavioral alterations.     

High-Resolution Proton Magnetic Resonance Analysis of Human Cerebrospinal Fluid

High-resolution proton magnetic resonance spectroscopy was used to analyze human cerebrospinal fluid obtained from patients with several neurological problems. The major metabolites measured included glucose, lactate, glutamine, citrate, inositol, acetate, creatine, creatinine, beta-hydroxybutyrate, alanine, and pyruvate. A drug vehicle, propylene glycol, was also measured. Alterations in the cerebrospinal fluid of these metabolites provided information concerning metabolism of the brain. Magnetic resonance spectroscopy offered a simple and rapid means of assessing these and other exogenous and endogenous compounds in diseases affecting the nervous system.     

Genetic reconstruction and functional analysis of the repeating lipoyl domains in the pyruvate dehydrogenase multienzyme complex of Escherichia coli

The dihydrolipoamide acetyltransferase component (E2p) of the pyruvate dehydrogenase complex of Escherichia coli contains three highly homologous sequences of about 100 residues that are tandemly repeated to form the N-terminal half of the polypeptide chain. All three sequences include a lysine residue that is a site for lipoylation and they appear to form independently folded functional domains. These lipoyl domains are in turn linked to a much larger (about 300 residues) subunit-binding domain of the E2p chain that aggregates to form the octahedral inner core of the complex and also contains the acetyltransferase active site. In order to investigate whether individual lipoyl domains play different parts in the enzymic mechanism, selective deletions were made in vitro in the dihydrolipoamide acetyltransferase gene (aceF) so as to excise one or two of the repeating sequences. This was facilitated by the high degree of homology in these sequences, which allowed the creation of hybrid lipoyl domains that closely resemble the originals. Pyruvate dehydrogenase complexes incorporating these genetically reconstructed E2p components were purified and their structures were confirmed. It was found that the overall catalytic activity, the system of active site coupling, and the ability to complement pyruvate dehydrogenase complex mutants, were not significantly affected by the loss of one or even two lipoyl domains per E2p chain. No special role can be attached thus far to individual lipoyl domains. On the other hand, certain genetic deletions affecting the acetyltransferase domain caused inactivation of the complex, highlighting particularly sensitive areas of that part of the E2p chain.     

Thermodynamic and kinetic considerations of Q-cycle mechanisms and the oxidant-induced reduction of cytochromesb

In coenzyme Q-cycles, it is proposed that one electron from the quinol reduces the Rieske iron sulfur center (E _m280 mV) and the remaining electron on the semiquinone reduces cytochromeb _T (E _m–60 mV). TheE _mfor the two-electron oxidation of the quinol is 60 mV and therefore the reduction of cytochromeb _T by quinol is not favorable. As the stability constant for the dismutation of the semiquinone decreases, the calculatedE _mfor the Q/QH couple is lowered to values below theE _mof cytochromeb _T. Contemporary coenzyme Q-cycles are based on the belief that the lower value for theE _mof the Q/QH couple compared to theE _mfor cytochromeb _T means that the semiquinone is a spontaneous reducing agent for theb-cytochrome. The analysis in the paper shows that this is not necessarily so and that neither binding sites nor ionization of the semiquinoneper se alters this situation. For a Q-cycle mechanism to function,ad hoc provisions must be made to drive the otherwise unfavorable reduction of cytochromeb _T by the semiquinone or for the simultaneous transfer of both electrons to cytochromeb _T and cytochromec ₁ (or the iron sulfur protein). Q-cycle mechanisms with these additional provisions can explain the observation thus far accumulated. A linear path which is functionally altered by conformational changes may also explain the data.     

The electrochemical H+ gradient in the yeastRhodotorula glutinis

The electrochemical gradient of protons, , was estimated in the obligatory aerobic yeastRhodotorula glutinis in the pH₀ range from 3 to 8.5. The membrane potential, , was measured by steady-state distribution of the hydrophobic ions, tetraphenylphosphonium (TPP⁺) for negative above pH₀ 4.5, and thiocyanate (SCN^–) for positive below pH₀ 4.5. The chemical gradient of H⁺ was determined by measuring the chemical shift of intracellular P_i by³¹P-NMR at given pH₀ values. The values of pH_i increased almost linearly from 7.3 at pH₀ 3 to 7.8 at pH₀ 8.5. In the physiological pH₀ range from 3.5 to 6, was fairly constant at values between 17–18 KJ mol^–1, gradually decreasing at pH₀ above 6. In deenergized cells, the intracellular pH_i decreased to values as low as 6, regardless of whether the cell suspension was buffered at pH₀ 4.5 or 7.5. There was no membrane potential detectable in deenergized cells.     

1H NMR study of the interaction of bacteriophage λ Cro protein with the O R 3 operator

The 17 base pair operator O _R ³ oligonucleotide, which is the preferential binding site for the Cro repressor of phage , was studied by two-dimensional NMR spectroscopy. A sequential assignment procedure based on two-dimensional Nuclear Overhauser Effect (NOESY) and scalar coupling correlated (COSY) NMR spectroscopy, together with the knowledge of the oligodesoxynucleotide sequence, made it possible to assign the non-exhangeable base protons and the H1 and the H2-H2 sugar protons of the O _R ³ operator DNA. The pattern of the observed NOE connectivities is consistent with a right-handed helical DNA structure. The base and sugar proton assignments provide the necessary information for further studies of the O _R ³ operator — Cro repressor interaction.Abbreviations COSY correlated spectroscopy - FID free induction decay - NOE nuclear Overhauser effect - NOESY nuclear Overhauser effect spectroscopy - RD relaxation delay - TSP sodium 3-trimethylsilyl-(2,2,3,3-²H₄)propionate - EDTA sodium ethylendiamine tetraacetate     

Zinc is a constituent of bovine heart cytochrome c oxidase preparations

Cytochrome c oxidase preparations from bovine heart muscle contain 1 zinc per 2 irons. Metal contents of nine preparations determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) show that Cu, Fe and Zn are the only metals present in significant amounts with average Cu/Fe, Fe/Zn, and Cu/Zn atom ratios of 1.3, 2.1 and 2.8, respectively. Removal of adventitious copper results in a Cu:Fe:Zn stoichiometry of 2:2:1. The zinc is tightly bound. Dialysis against a solution of 1,10-phenanthroline at pH 7.4 or an acidic buffer (pH 4.4) does not remove Zn. Dialysis against 0.8 M KCN at pH 10 causes partial loss of both Cu and Zn. This is the first evidence for the presence of Zn in a cytochrome c oxidase.     

In vitro metabolism of N-methyl-dibenzo [c,g]carbazole a potent sarcomatogen devoid of hepatotoxic and hepatocarcinogenic properties

The metabolism of N-methyl substituted 7H-dibenzo[c,g]carbazole (N-Me DBC) was investigated in vitro using liver microsomes from 3-methylcholanthrene (MC)-, benzo[c]carbazole (BC) and Arochlor-pretreated mice and rats. N-Me DBC is a potent sarcomatogen devoid of hepatotoxicity and liver carcinogenic activity. The ethyl acetate-extractable metabolites were separated by high performance liquid chromatography (HPLC) and most of them were identified by proton magnetic resonance (PMR), mass spectrometry (MS) and comparison with synthetically prepared specimens. Mouse and rat microsomes gave rise to the same metabolites. The major metabolites were 5-OH-N-Me DBC (50%), N-hydroxymethyl (HMe) DBC (25-30%) and 3-OH-N-Me DBC (10%). Addition of 1,1,1-trichloropropene-2,3-oxide (TCPO) to the standard incubation medium permitted the identification of two dihydrodiols among the minor metabolites. No metabolite of DBC was observed after incubation of N-Me DBC, or its major metabolite N-HMe DBC, with either mouse or rat microsomes, but the possibility of a slight demethylation cannot be totally excluded. The lack of biotransformation at the nitrogen atom site may explain the lack of hepatotoxicity and liver carcinogenic activity of N-Me DBC. The modulation of metabolism by epoxide hydrolase, cytosol and glutathione was also investigated. The results are discussed in the light of data previously obtained with hepatotoxic and hepatocarcinogenic DBC.