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PubMedDate not supplied

Identification of some human urinary metabolites of orally administered potassium canrenoate by stable isotope-labeling techniques.

A single oral dose (200 mg) of an equimolar mixture of potassium canrenoate and its 20,20,21,21-tetradeutero analogue was administered to three healthy men. The steroids in urine collected for 24 hr after dosage were isolated on XAD-2 resin, and purified and fractionated into groups by lipophilic gel chromatography before and after hydrolysis of conjugates. GC/MS analysis of these fractions allowed the detection and identification of canrenone, canrenoic acid and its ester glucuronide, 3 beta-hydroxy-3-deoxocanrenone, 3beta-hydroxy-4,5alpha-dihydro-3-deoxocanrenone and a 3epsilon-hydroxy-4,5,6,7-tetrahydro-3-deoxocanrenone. In addition a number of di- and trihydroxy compounds formed by reduction and hydroxylation were partially identified from their E1 and C1 mass spectra. The results provide information on the metabolism of oral potassium canrenoate in man, and demonstrate the utility of combining stable isotope labeling, lipophilic gel chromatography, and GC/MS in studies of steroidal spirolactones.

Administration, Oral↗
PubMed1979

[Photo-oxidation and carboxymethylation of guanylribonuclease Pch1].

The effect of photo-oxidation and carboxymethylation on the activity of RNAse Pch1 has been studied. Photoinactivation in the presence of rose bengal results in a selective oxidation of two histidine residues. The process is inhibited by the nucleotide substrate analogs. This suggests that one or two imidazole groups may be localized in the active site of RNAse Pch1. The pH dependence of the enzyme inactivation by bromoacetic acid is indicative of the contribution of a functional group with pKa 4,0, presumably of a beta- or gamma-carboxyl group of dicarbonic amino acid. The reaction is inhibited by the substrate analogs 2'(3')-GMP and 2'(3')-AMP. The data on the similarity of active sites in several guanyloribonucleases are discussed.

Histidine↗
PubMedDate not supplied

[2-14C-phenazepam metabolism in vitro].

Phenazepam undergoes aromatic and C3-hydroxylation in the microsomes of albino rats. Saturation of phenazepam oxidising enzymes proceeds at different substrate concentrations for both processes. Interaction of cytochrome P-450 with phenazepam is accompanied by spectral changes in the type II hemoprotein.

Animals↗
PubMed1979

NMR studies of the quaternary structure and heterogeneity of nitrosyl- and methemoglobin.

NMR was used to study the quaternary structure of nitrosyl- and methemoglobin, the kinetics and equilibrium behavior of nitric oxide binding, and the oxidation of hemoglobin. The -9.6 ppm (from H2O) resonance was used as a measure of nitrosylhemoglobin molecules in the T quaternary structure. We found that stripped nitrosylhemoglobin is 70% in the T state below pH 6.4, and is in the R state above. Inositol hexaphosphate (IHP) raises this transition point to pH 7.5. For stripped aquomethemoglobin, the T marker at -10 ppm is absent. In IHP, at pH 6.5 all of the molecules are in the T state. At both higher and lower pH they shift to the R state. The intensity decreases to half of its maximum at pH 5.5 and 7.4. The relative affinity of nitric oxide binding to the alpha and beta subunits was inferred from the intensities of the resonances at -12 and -18 ppm. Under conditions in which nitrosylhemoglobin exists in the T state, NO binds to the alpha subunit 10 times more strongly than it does to the beta subunit. The kinetic experiments reveal that it binds to the two subunits at the same rate and that it dissociates at 5 x 10(-3) s-1 from the beta subunit and at 5 x 10(-4) s-1 from alpha subunit. At high pH, the two subunits are ligated at the same rate. Potassium ferricyanide oxidation, at pH 6.0 in the absence of IHP, is about 3 times more favorable for the alpha than the beta subunit. Addition of IHP raises this preferential oxidation slightly. At pH 8.44, both alpha and beta subunits were oxidized at the same rate.

Adult↗
PubMed1978

[Heterogeneity and regulation of glutamate dehydrogenase activity in mammalian brain and liver].

The present report concerns the study of the catalytic properties and the coenzyme affinity of glutamate dehydrogenase (GDH) and its isoenzymes in various preparations of the brain and liver as well as the different regulatory mechanisms controlling the ratio of the rates of biogenesis and breakdown of glutamate (Glu). The investigations carried out showed that GDH activity of various preparations of brain and liver (crystalline enzymes, cellular extracts and mitochondria) are markedly different from each other by their catalytic and regulatory properties as well as by their coenzyme activity. The data obtained make us conclude that nicotinamide-hypoxanthine-nucleotide (deaminoNAD) is a more effective coenzyme in the oxidative deamination of Glu, than other piridine nucleotides (NAD, NADP, deamino-NADP). It is supposed that in the formation of ammonia and amino acids in brain and especially liver, together with other known mechanisms an important role may be ascribed to the process of transdeamination. In this aspect, as a co-factor of oxidative deamination of Glu deamino-NAD (D-NAD) is thought to be of significant importance.

Animals↗
PubMed1979

[Mitochondrial transhydrogenase: general principles of functioning].

A new mechanism for the functioning of mitochondrial transhydrogenase has been proposed. This mechanism makes it possible, without additional postulates, to explain the generation of delta muH+ of different signs in the forward and reverse transhydrogenase reactions and why this generation is not accompanied by the membrane uncoupling. It is suggested that the reduced nicotinamide rings of NADH and NADPH participate in a relay transfer of H+ ions across the membrane, while the oxidized nicotinamide rings of NAD+ and NADP+ block the H+-transporting paths in the transhydrogenase.

Animals↗
PubMed1979

[Comparative study of effects of the tyrosine-copper(II) complex on xenobiotic hydroxylation and lipid peroxidation].

It has been found that NADPH-dependent hydroxylation of dimethylaniline, aniline, p- and o-nitroanisol and lipid peroxidation is inhibited by the tyrosine-copper (II) complex (low molecular weight analog of superoxide dismutase), which is indicative of a possibility of superoxide radicals formation in these reactions. The inhibition of the above-mentioned reactions with Tyr2-Cu2+ is less pronounced or absent, if cumole hydroperoxide is used as cosubstrate instead of NADPH. Differences in the Tyr2-Cu2+ complex effects on the cumule hydroperoxide-dependent xenobiotics hydroxylation and lipid peroxidation catalyzed by various forms of cytochrome P-450, e. g. microsomal, soluble and incorporated into liposomes, have been found. The data obtained suggest that the efficiency of the inhibitory effect of the Tyr2-Cu2+ complex depends on the type of cosubstrates (NADPH, cumole hydroperoxide) and substrates used as well as on the form of cytochrome P-450.

Animals↗
PubMed1979

[Shifts of the bacteriochlorophyll absorption band at 880 nm in chromatophores and subchromatophore pigment-protein complexes from Rhodospirillum rubrum].

The redox potential dependency of the light-induced absorption changes of bacteriochlorophyll in the chromatophores and subchromatophore particles from Rhodospirillum rubrum has been studied. The highest values of the absorption changes due to the bleaching of P870 and the blue shift of P800 are observed within the redox potential range of 360--410. At the potential values below 300 mV the 880 nm band of bacteriochlorophyll shifts to shorter wavelengths in the subchromatophore particles and to longer wavelengths in the chromatophores. Redox titration revealed that the red and blue shifts of 880 nm bacteriochlorophyll band are caused by the functioning of a non-identified component (X) which has an oxidation -- reduction midpoint potential close to 340 mV (n = 1) within the pH range of 6,0--7,6. The Em for this component decreases by 60 mV/pH unit within the pH range of 7.6--9,2. The results obtained suggest that the red shift is due to the transmembrane, while the blue shift -- to the local intramembrane electric field. The generation of both the transmembrane and local intramembrane electric fields apparently depends on redox transitions of the component X.

Bacterial Chromatophores↗
PubMed1979

Reduction of anthracycline glycoside by NADPH--cytochrome P-450 reductase.

The in vitro degradation of the new antitumor anthracycline antibiotic, aclacinomycin-A, was studied using rat liver homogenate. In the presence of NADH or NADPH, the glycosidic bond at C-7 position of aclacinomycin-A was reductively cleaved to produce 7-deoxyaklavinone and 7-deoxyaklavinone dimer, MA144 E1. Subcellular fractionation indicated that most of the enzyme activity was present in the microsomal fraction and required anaerobic condition and NADPH. The purified enzyme reduced the glycosidic metabolites, MA144 M1 and MA144 N1, as well as aclacinomycin-A. The optimum pH for the anthracycline glycoside reductase reaction using aclacinomycin-A as substrate was 7.4. The enzyme was sigmoidally saturated with aclacinomycin-A and showed the concentration of 1.2 x 10(-4) M required for half maximal activity, and Km value of 7.7 x 10(-5) M for NADPH. The degradative pathway of aclacinomycin-A and its glycosidic metabolites was discussed.

Anaerobiosis↗
PubMed1979

Kinetics of elementary steps in the cytochrome P-450 reaction sequence. III. NADPH reduction of cytochrome P-450LM at different integrational levels.

The aerobic NADPH reduction of cytochrome P-450LM has been investigated on microsomes, as well as on the solubilized enzyme system in the associated, disintegrated, and reconstituted state, respectively. P-450 exhibits biphasic reduction kinetics of about 70/30% phase distribution and rate constants differing 10-fold. The partial reactions are due to organizational asymmetries, the cytochrome being either incorporated into P-450/reductase associates (cluster) or localized outside (randomly distributed, homoassociated, weakly cluster-associated). Triton N-101 disintegrates the different associate structures, consequently followed by the disappearance of the rapid reaction phase. The enzyme system can be reconstituted; at microsomal stoichiometry the respective standard parameters are approached, depending on the composition and structural organization of the phospholipid. The reorganization without any membrane matrix is obviously thermodynamically determined.

Animals↗