On the mechanism of action of cytochrome P450: evaluation of hydrogen abstraction in oxygen-dependent alcohol oxidation

The mechanisms of oxidation of primary and secondary benzylic alcohols to the corresponding carbonyl compounds by purified rabbit liver cytochrome P450 forms 2B4 and 2E1 in a reconstituted enzyme system has been examined by linear free energy relationships, intramolecular and steady-state deuterium isotope effects, and the incorporation of an O2-derived oxygen atom or solvent-derived deuterium. The kcat and Km values were found to be relatively insensitive to the presence of electronic perturbations at the para position. The Hammett reaction constants for the oxidation of benzyl alcohols by P450s 2B4 and 2E1 are -0.46 and -0.37, respectively, and with 1-phenylethyl alcohols the corresponding reaction constants are -1.41 and -1.19, respectively. With [1-2H1]benzyl alcohol, P450s 2B4 and 2E1 show similar intramolecular deuterium isotope effects of 2.6 and 2.8, respectively, whereas with [1-2H2]benzyl alcohol under steady-state conditions, the deuterium isotope effects on the catalytic constants are 2.8 and 1.3, respectively. No significant isotope effect on the catalytic constant was noted for either form of P450 with 1-phenylethyl alcohol. In D2O, acetophenone formed by either form of P450 from 1-phenylethyl alcohol does not contain a deuterium atom at the methyl group, whereas under an atmosphere of 18O2 approximately 30% of the labeled oxygen is incorporated into the carbonyl group with either form of the cytochrome. The results are consistent with a mechanism that involves stepwise oxidation of the alcohol to a carbon radical alpha to the alcohol function, followed by oxygen rebound to yield the gem-diol, dehydration of which gives the carbonyl product.(ABSTRACT TRUNCATED AT 250 WORDS)

Bromophenacyl bromide binding to the actin-bundling protein l-plastin inhibits inositol trisphosphate-independent increase in Ca2+ in human neutrophils

Ligation of IgG Fc receptors on polymorphonuclear leukocytes causes an increase in the concentration of free intracytoplasmic Ca2+ ([Ca2+]i) which arises from release of intracellular stores but is independent of inositol 1,4,5-trisphosphate. We found that bromophenacyl bromide (BPB), an alkylating agent which inhibits leukocyte degranulation, adherence, and phagocytosis, inhibited IgG-stimulated increases in [Ca2+]i with an IC50 of 0.2 microM. In contrast, BPB had no effect on inositol 1,4,5-trisphosphate-dependent [Ca2+]i increases induced by fMet-Leu-Phe, complement fragment C5a, ATP, or platelet-activating factor. Using a monoclonal antibody specific for BPB, we identified in polymorphonuclear leukocytes a single cytosolic protein of 66 kDa and isoelectric point pH 5.6 which bound BPB when intact cells were treated with the alkylating agent. This BPB-binding protein was identified as l-plastin, a Ca(2+)-regulated actin-bundling protein. l-Plastin was found associated with the Triton X-100-insoluble cytoskeleton in polymorphonuclear leukocytes adherent to immune complexes, suggesting that BPB affects Fc receptor-mediated signal transduction by altering the actin cytoskeleton. Consistent with this hypothesis, both cytochalasin B and cytochalasin D inhibited the IgG-dependent increase in [Ca2+]i, without any effect on fMet-Leu-Phe-induced Ca2+ release. These data suggest that the actin cytoskeleton is essential for signal transduction from plasma membrane Fc receptors and that l-plastin has a critical role in activation of this pathway.

p-Bromophenacyl bromide modification of Bothrops asper myotoxin II, a lysine-49 phospholipase A2, affects its pharmacological activities

Modification of Bothrops asper myotoxin II, a lysine-49 phospholipase A2 variant, was carried out with p-bromophenacyl bromide. Modified toxin did not show changes in its charge and immunological properties but two of its pharmacological activities were modified. Myotoxic activity, measured by histology and by increment of creatine kinase levels in plasma of mice, was significantly reduced after toxin modification. In addition, liposome disruption activity was also significantly lower with the modified toxin both at 3 and 24 hr of incubation with the alkylating reagent. Some of the implications of these results on the structure-function relationship of myotoxins are discussed.

[Changes in basic nitrogen in a group of potential new beta- adrenolytics--derivatives of p-hydroxyacetophenone and p-hydroxypropiofenone]

Within the relationship of the structure and effect of new beta-adrenolytic agents derivatived from p-hydroxyacetophenone and p-hydroxypropiophenone with a propoxymethyl group in the lipophilic part of the molecule and with a propanamine, a butanamine and a pyrrolidine in the side-chain were studied. In order to prepare these substances, a procedure was selected from several tested ones, in which 4-hydroxy-3propoxymethylphenylketone were treated with chloromethyloxirane and subsequent reaction a hydrobromic acid were prepared 4-(3-brom-2-hydroxypropoxy)-3-propoxymethylalkylketone. Final substances were prepared reaction with amine. The structure of prepared compounds was confirmed on the basic interpretation of the IR, UV and 1H NMR spectra. The results of pharmacological evaluation of selected compounds showed a significant beta 1-blocking activity lower than acebutolol. Their local anesthetic activity is low according with their partition coefficients. The characteristic of the prepared compounds was supplemented by the determination of their partition coefficients, surface tension, dissociation constants and acute toxicity.

Strategies in pathogenesis: mechanistic specificity in the detection of generic signals

The virulence genes of the plant pathogen Agrobacterium tumefaciens are induced by more than 40 low-molecular-weight phenolic compounds. The prevailing opinion is that (i) wound-derived phenols produced on breach of the integrity of the cell wall act as the initiating signal in a series of events which results in host cell transformation, and (ii) a classical membrane receptor, putatively VirA, is responsible for the recognition of all such phenolic inducers. Here, we argue that the discovery of the subset of inducers that are relatives of the dehydrodiconiferyl alcohol glucoside (DCG) growth factors redirects our attention to work on the plant wound as a site of cell division, and suggests that we further explore the implications of early work on the relationship between transformation efficiency and the status of the cell cycle of the host. In addition, we argue that the significant structural diversity allowed in the para position of the phenol ring of inducers suggests that a receptor-ligand interaction based solely on structural recognition is insufficient, but that recognition followed by a specific proton transfer event may be sufficient to explain vir induction activity. Hence, the specificity of the response of A. tumefaciens may be a consequence of the features required for a chemical reaction to occur on the receptor surface. Finally, we review affinity labelling studies which exploit this phenol detection mechanism and which provide evidence that the phenol receptor may be other than VirA, the sensory kinase of the two component regulatory system implicated in Agrobacterium virulence.(ABSTRACT TRUNCATED AT 250 WORDS)

Study of photodynamic reactions of p-nitroacetophenone using ESR and optical techniques

The photosensitizing properties of p-nitroacetophenone (PNAP), a well-known radiosensitizer, have been studied in near UV region. The mechanism of PNAP photosensitization has been investigated by testing the efficiency of singlet oxygen production using photooxidation of 2,2,6,6-tetramethylpiperidine (TEMP) and photodegradation of guanosine. In both the cases, the enhancement effect of deuterated solvents has been observed. Results of these experiments suggest the significant role of type II mechanisms in PNAP photosensitization.

Constituents of the roots of Cynanchum bungei Decne. Isolation and structures of four new glucosides, bungeiside-A, -B, -C, and -D

Four new glucosides, bungeiside-A, -B, -C, and -D, were isolated from the roots of Cynanchum bungei Decne. The structures of the new compounds were determined by chemical and spectroscopic methods, including two-dimensional nuclear magnetic resonance (2D NMR) techniques, especially 1H-detected heteronuclear multiple-bond multiple-quantum coherence.

Unexpected racemization of proline or hydroxy-proline phenacyl ester during coupling reactions with Boc-amino acids

When L-proline or O-benzyl-trans-4-hydroxy-L-proline phenacyl ester was coupled with Boc-amino acids in dimethylformamide using water-soluble carbodiimide (WSCI) in the presence of anhydrous 1-hydroxybenzotriazole (HOBt) as coupling reagents, extensive racemization was observed at the C alpha of the proline or hydroxy-proline residue. The extent of racemization was measured by HPLC after the coupling with Boc-L-Leu-OH in the presence or absence of HOBt. The extent of racemization increased when HOBt was added to the reaction mixture, but greatly decreased when it was not, indicating that HOBt was needed for inducing racemization. Almost no racemization was observed when the coupling reaction was carried out by the mixed anhydride procedure in tetrahydrofuran or by the carbodiimide method in dichloromethane without using HOBt. In the case of coupling reactions with ordinary L-amino acid phenacyl esters, no racemization was observed. Examination of some model systems yielded sufficient evidence to prove that HOBt is an efficient catalyst for racemizing proline or hydroxy-proline phenacyl ester not only in the stage of cyclic intermediate formation but also in the opening of the ring structure. Thus, the racemization reaction was found to be closely related to the formation of the cyclic carbinol-amine derivative.

High-performance liquid chromatographic determination of biotin in biological materials after crown ether-catalyzed fluorescence derivatization with panacyl bromide

This paper reports a high-performance liquid chromatographic (HPLC) technique to determine biotin in biological samples. Biotin and the internal standard dethiobiotin are converted into fluorescent derivatives by using panacyl bromide [p-(9-anthroyloxy)phenacyl bromide] as a fluorescence label. Biotin is extracted from biological tissue with trichloroacetic acid and the extract is purified by a combination of solid-phase extraction on C18 cartridges, ion-exchange chromatography on DOWEX formate resin, and thin-layer chromatography. The purified sample extract is derivatized in the presence of a crown ether. The resulting panacyl esters can be separated on reversed-phase as well as on normal-phase HPLC. Normal phase HPLC is preferable because it provides higher sensitivity and demands less sample pretreatment. Analysis of rat intestinal tissue revealed that only about 13% of the biotin is present in free form whereas 87% is bound in proteins from which it can be released by hydrolysis. Biotin values determined by this method are comparable to those obtained by other techniques.

OVID and SUPER: two overlap programs for drug design

Two programs, OVID and SUPER, for exploring the similarity of molecules with respect to their action at a receptor are described. OVID accepts two molecules as input and optimizes the three-dimensional overlap of specified atoms in one molecule with specified atoms in the second molecule. The result is expressed as a percent of the theoretical maximum. OVID gives a quantitative measure of the extent of a guessed correspondence between two molecules based on volume overlap of selected atoms. The Achilles' heel of OVID is that the correspondence between the two molecules has to be guessed. We realized that it would be better to systematically examine all possible correspondences of two structures to minimize the chance of overlooking a superior correspondence. We created SUPER to satisfy this need. SUPER accepts two molecules as input and finds the top twenty correspondences of their surfaces and charge distributions, giving a quantitative measure of the extent of each correspondence. An instructive example of the application of OVID and SUPER to the design of leukotriene D4 receptor antagonists is described. SUPER appears to be a practical brain-storming tool for the medicinal chemist trying to understand how molecules whose structures may not resemble one another in an obvious way can bind to the same site.

Identification of aromatic moieties and mycosamine in antifungal heptaenes with high-performance liquid chromatography, high-performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry

A high-performance liquid chromatographic (HPLC) method for the determination of the aromaticity of heptaene polyene antibiotics has been developed. The released aromatic moiety of the heptaene polyenes aureofungin, candicidin, candimycin, hamycin and trichomycin was assayed after alkaline hydrolysis. The presence of p-aminoacetophenone (PAAP) and N-methyl-p-aminoacetophenone (N-methyl-PAAP) in the hydrolysates was determined by HPLC, HPLC-mass spectrometry (HPLC-MS) and gas chromatography-MS (GC-MS). Candicidin and hamycin contained only the PAAP residue; aureofungin contained both PAAP and N-methyl-PAAP. Trichomycin contained PAAP and also some unknown component of molecular weight 179. The aromatic nature of the individual components of the heptaene complex was demonstrated using radioactivity flow detection for the determination of the incorporation of [14C]-p-aminobenzoic acid to individual candicidin components. Ammonia chemical ionization MS was successfully used for the GC-MS identification of the acetylated mycosamine moiety of heptaenes.

Measurement of plasma acetate kinetics using high-performance liquid chromatography

Previous studies suggest that plasma acetate may be an important fuel in man, accounting for approximately 10% of energy expenditure. Available methods for the determination of plasma acetate kinetics are difficult and time consuming. We describe here a procedure for the determination of plasma acetate concentration and specific activity using automated high-performance liquid chromatography that is precise and sensitive and accommodates large numbers of samples. The procedure involves extraction from plasma with diethyl ether, derivatization with bromoacetophenone, and separation on a C-18 reversed-phase column. The specific activities of D-beta-hydroxybutyrate and lactate can also be determined. Acetate turnover was measured in four dogs and was similar to that previously reported in sheep and humans. Transport of [14C]acetate into red blood cells was negligible.

(Phenylmethoxy)phenyl derivatives of omega-oxo- and omega-tetrazolylalkanoic acids and related tetrazoles. Synthesis and evaluation as leukotriene D4 receptor antagonists

Two series of (phenylmethoxy)phenyl compounds derived from the structure of LY163443 were synthesized and evaluated as leukotriene D4 receptor antagonists. In the omega-[(phenylmethoxy)phenyl]-omega-oxoalkanoic acid series, 5-[4-[(4-acetyl-2-ethyl-3-hydroxyphenyl)methoxy]phenyl]-3,3-dimethyl-5- oxopentanoic acid (8) was the most potent antagonist of LTD4-induced contractions of guinea pig ileum (pKB of 7.60) and LTD4 pressor response in pithed rats (ED50 of 1.4 mg/kg iv). Replacing the carboxylic acid function with 5-tetrazole gave slightly more potent compounds. In the omega-[5-[[(phenylmethoxy)phenyl]alkyl] tetrazolyl]alkanoic acid series, replacing the carboxylic acid with 5-tetrazole gave compounds that were equally effective in the guinea pig ileum but more potent in vivo against the LTD4 pressor response in rat. The pKB value in the guinea pig ileum for 1-[2-hydroxy-3-propyl-4- [[4-[[2-[3-(1H-tetrazol-5-yl)propyl]-2H-tetrazol-5-yl]methyl ] phenoxy]methyl]phenyl]ethanone (25) was 7.87 and the ED50 for antagonism of the LTD4 pressor response was 4.0 mg/kg iv. The sodium salts of 8 (9) and 25 (26) given by the iv route of administration antagonized LTD4-induced cardiovascular alterations in anesthetized rat and LTD4-induced bronchoconstriction in guinea pig in a dose-dependent manner. Oral activity was also demonstrated against the LTD4-induced bronchoconstriction in guinea pig.

Effect of linking allyl and aromatic chains to histidine 170 in horseradish peroxidase

Histidine residues in horseradish peroxidase (HRP) were modified chemically with diethyl pyrocarbonate, 4,omega-dibromoacetophenone or diallylpyrocarbonate. Histidines were chosen as His-170, the fifth ligand of the heme iron atom, forms part of the active site of this enzyme. Good yields of hemoprotein were obtained in all cases. Analysis by HPLC of peptides obtained after tryptic digestion showed that His-170 of HRP was in fact modified. The specific activity remained satisfactory after chemical modification of the histidine residues, and so the active site of HRP can thus be altered without a dramatic loss of hemoprotein or peroxidase activity. This may open routes to the preparation of novel biocatalysts.

[Amphoteric ion intermediates in the pyrazine series. II. The action of p-nitrophenacyl bromide on pyrazine]

Continuing to present the results of the investigations carried out on the amphoteric ions intermediates of the N-heteroatomic system with 2 natrium atoms in positions 1, 4, new pyrasine derivatives synthetized with p-nitro-phenacyl bromide are described. The observations on their antimicrobial and antiyeast activities is discussed.