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PubMed1996

A column centrifugation method for the reconstitution in liposomes of the mitochondrial F0F1 ATP synthase/ATPase.

A method for reconstitution of membrane proteins into unilamellar liposomes is described. The model enzyme was the F0F1 ATP synthase from mitochondria when in complex or free from its inhibitor protein. The enzymes were first solubilized with either of two detergents, i.e., n-dodecyl-beta-D maltoside or lauryldimethylamine oxide. After solubilization, the enzymes were passed through a column of Sepharose-AH using an ADP/sodium cholate selective elution buffer. The enzymes recovered from the column were subsequently passed through a centrifuge column of Sephadex G-50 fine. The eluate contained liposomes in which the F0F1 complex (with and without inhibitor protein) had been reconstituted. The reconstituted enzymes were capable of hydrolyzing ATP with formation of electrochemical H+ gradients. They also catalyzed the ATP-Pi exchange reactions. Thus the F0F1 complex which is formed by 18 subunits can be rapidly reconstituted into liposomes in a fully functional state. Moreover the data show that the interactions between the enzyme and its inhibitor protein are not perturbed in the reconstitution procedure.

Animals↗
PubMed1997

The involvement of cytochrome P450 3A4 in the N-demethylation of L-alpha-acetylmethadol (LAAM), norLAAM, and methadone.

The N-demethylation of LAAM, norLAAM, and methadone has been investigated in human liver microsomes and microsomes containing cDNA-expressed human P450s. Gas chromatography/mass spectrometry methods allowed detection of norLAAM and dinorLAAM formation from LAAM, dinorLAAM formation from norLAAM, and EDDP and EMDP formation from methadone. The rates of N-demethylation varied 4- to 7-fold in microsomes from four different donors with activities for LAAM and norLAAM consistently greater (5- to 14-fold) than for methadone. The N-demethylation of LAAM, norLAAM, and methadone were significantly inhibited by ketoconazole. IC50s could be determined for ketoconazole inhibition of LAAM and norLAAM N-demethylation of 1.6 and 1.1 microM, respectively. The ability of ketoconazole to reduce methadone N-demethylation below 40% varied in regard to liver donor. No other P450-selective inhibitors reduced the average activities more than 43%. cDNA-expressed P450 3A4 N-demethylated LAAM, norLAAM, and methadone at greater rates than the other cDNA-expressed P450s studied (1A2, 2C9, 2D6, or 2E1). P450 3A N-demethylation of LAAM, norLAAM, and methadone exceeded the next most active P450, respectively, by at least 2.5, 9.6, and 13.4 times when expressed per milligram protein and by 18.2, 6.0, and 6.1 times when expressed per nanomole P450. These results suggest that P450 3A4 is the primary site of N-demethylation of LAAM, norLAAM, and methadone in human liver. Although other enzymes may also be capable of N-demethylating these compounds, identification of specific enzymes, except P450 3A4, has yet to be established. Knowledge of these enzymatic pathways is essential for assessment of the impact of metabolic drug-drug interactions on therapeutic success and/or adverse events.

Cytochrome P-450 CYP3A↗
PubMedDate not supplied

[Role of the hydrophobicity of polymethylene-bis-quaternary ammonium compounds in the mechanism of their curare-like action].

Lengthening of the N-alkyl radical (from--C2H5 to C10H21) in the series of polymethylene-bis-quaternary ammonium compounds was found to result in an increased hydrophobic properties of the compounds. In the presence of the N-butyl radical the mode of the action exerted by the substances changes, viz. from depolarizing they turn into antidepolarizing ones. A substitution of polyalicyclic radicals (cyclohexyl, 1-adamantyl) for methyl groups at the nitrogen atoms in the series of polymethylene-bis-quaternary ammonium compounds proved that in order to changed the mode of action hydrophobic properties of the cyclohexyl radicals appear to be good enough.

Animals↗
PubMedDate not supplied

Rapid determination of volatile bases in fish by using an ammonia ion-selective electrode.

A simple and rapid method using an ammonia ion-selective electrode (ISE) to measure volatile bases in fish is proposed. Accuracy and precision were determined with 5, 10, 20, and 30 ppm NH3 standard solutions. Ammonia values obtained with the method correlate strongly with total volatile basic nitrogen (r2 = 0.88). Recoveries of added ammonia to homogenized fish samples ranged from 83.7 to 96.0%. Responses of the probe to trimethylamine (TMA), calculated as NH3 (mg/100 mL), ranged from 74.9 to 91.7%. These findings indicate that the probe measured TMA as well as ammonia. Storage trials on 8 fish species illustrated that the results obtained with the ISE method reflected nitrogen concentrations based on total volatile base (TVB) analysis. This procedure may be used in lieu of the traditional TVB method for on-site rapid screening of fish.

Ammonia↗