Acetylamino Group Research Articles

Simple and Rapid Spectrophotometric Determination of Trace Titanium(IV) with Preconcentration as Its Anionic Tiron Chelate on Chitin.

The spectrophotometric methods for the determination of microamounts of titanium have been based on the complexes with hydrogen peroxide', 1,2-dihydroxybenzene-3,5-disulfonate (tiron)2'3, chromotropic acid4'5 and diantipyrylmethane.6'' These methods have comparatively high selectivity but low sensitivity. Therefore, attempts have been made to enhance the sensitivity by combination with preconcentration methods for the determination of traces of titanium, including solvent extractiong- and solid-phase extraction on supports such as membrane filter'2,'3, ion-exchange resin14 and naphthalene. l s The spectrophotometric, atomic absorption spectrometric and electroanalytical methods for many inorganic ions have been developed by using the collection process on chitin after their ions are converted into each suitable species such as colored metal complexes or anionic species. 16-30 Chitin, which is a natural amino polysaccharide and a hydrophilic polymer similar to cellulose, but is stable over a wide pH range of aqueous solution, has the excellent properties as the support for solid-phase extraction: namely, the collection and elution of species is rapidl6-'9, and its protonated acetylamino groups act as anion-exchangers for various type of anionic species in weak acidic medium.20-29 In this paper we report on the spectrophotometric determination of trace amounts of titanium(IV) following the preconcentration procedures as follows: first the collection as its anionic tiron chelate on protonated chitin, and second the elution with a small volume of ammonia buffer solution. The proposed method was applied to the determination of titanium in environmental samples.

1H and 13C NMR spectral assignments of the major sequences of twelve systematically modified heparin derivatives

The complete 1H and 13C NMR spectral assignments are described for the most prevalent patterns of sulfation and acetylation which can be found in polymeric heparin or can be obtained by standard chemical modifications. These include a number of novel structures containing unsubstituted or acetylated amino groups and the first complete NMR assignments of many of the other derivatives. Beef lung heparin was chosen as a model system and studies were carried out using conditions to control the influences on the chemical shift positions in heparin samples of divalent cations and variations in pH and temperature.

Participation of a medium chain acyl-CoA synthetase in glycine conjugation of the benzoic acid derivatives with the electron-donating groups

Glycine conjugation of a series of benzoic acid derivatives was investigated in bovine liver mitochondria. Benzoic acids with chlorine, methyl, methoxy, or ethoxy substituents in the para- or metapositions of the benzene ring showed a high degree of glycine conjugation. In contrast, the acids with cyano, nitro, amino, or acetylamino groups were conjugated to a small extent with glycine. A medium chain acyl-CoA synthetase that activates carboxylic acids was purified from bovine liver mitochondria. The purified medium chain acyl-CoA synthetase accepted not only medium chain fatty acids but also aromatic and arylacetic acids as substrates. There was a good correlation between the activity of the purified medium chain acyl-CoA synthetase and glycine conjugation of ten benzoic acids with electron-donating substituents. These findings indicate that the purified medium chain acyl-CoA synthetase is a major enzyme for glycine conjugation of benzoic acids with electron-donating groups in bovine liver mitochondria.

The intercellular adhesin involved in biofilm accumulation of Staphylococcus epidermidis is a linear beta-1,6-linked glucosaminoglycan: purification and structural analysis

The primary attachment to polymer surfaces followed by accumulation in multilayered cell clusters leads to biofilm production of Staphylococcus epidermidis, which is thought to contribute to virulence in biomaterial-related infections. We purified a specific polysaccharide antigen of biofilm-producing S. epidermidis 1457 and RP62A, which was recently shown to have a function in the accumulative phase of biofilm production by mediating intercellular adhesion (D. Mack, M. Nedelmann, A. Krokotsch, A. Schwarzkopf, J. Heesemann, and R. Laufs, Infect. Immun. 62:3244-3253, 1994). Following Sephadex G-200 gel filtration, this antigen was separated by Q-Sepharose chromatography into a major polysaccharide, polysaccharide I (> 80%), which did not bind to Q-Sepharose, and a minor polysaccharide, polysaccharide II (< 20%), which was moderately anionic. As shown by chemical analyses and nuclear magnetic resonance spectroscopy, polysaccharide I is a linear homoglycan of at least 130 beta-1,6-linked 2-deoxy-2-amino-D-glucopyranosyl residues. On average, 80 to 85% of them are N acetylated; the rest are non-N-acetylating and positively charged. Chain cleavage by deamination with HNO2 revealed a more or less random distribution of the non-N-acetylated glucosaminyl residues, with some prevalence of glucosaminyl-rich sequences. Cation-exchange chromatography separated molecular species whose content of non-N-acetylated glucosaminyl residues varied between 2 and 26%. Polysaccharide II is structurally related to polysaccharide I but has a lower content of non-N-acetylated D-glucosaminyl residues and contains phosphate and ester-linked succinate, rendering it anionic. Enzyme-linked immunosorbent assay inhibition with various monosaccharides revealed the beta-anomeric form and the acetylated amino group of the D-glucosaminyl residues as important for reactivity with the specific antiserum. The unbranched polysaccharide structure favors long-range contacts and interactions between polysaccharide strands and the cell wall and/or lectin-like proteins, leading to intercellular adhesion and biofilm accumulation. The structure of the polysaccharide is, so far, considered to be unique and, according to its function, is referred to as S. epidermidis polysaccharide intercellular adhesin (PIA).

Construction of α‐phosphonolactams via rhodium (II)‐catalyzed intramolecular CH insertion reactions

AbstractThe Rh(II)‐catalyzed intramolecular CH insertion reactions of N,N‐dialkyl‐α‐diazo‐α‐(diethylphosphono)acetamides 2a,f–j in CHCl3 or ClCH2CH2Cl were found to give monocyclic and bicyclic α‐phosphono‐β‐lactams, 3a and 3f–j, in 43–67% yields via regiospecific α‐CH insertion of the N‐alkyl groups. Similar treatment of N‐benzyl‐N‐isopropyl‐α‐diazo‐α‐(diethylphosphono)acetamide (2b) and the corresponding N‐isobutyl‐N‐methylacetamide 2d in ClCH2CH2Cl afforded mixtures of β‐lactams 3b (35%) and and 3b′ (16%), β‐lactam 3d (47%), and γ‐lactam 4d (10%), respectively, each of which is formed by the competitive CH insertion reaction between benzylic and isopropyl α‐CH bonds and between methyl α‐CH and methine β‐CH bonds, respectively. For the formation of β‐lactams, the selectivity in the rhodium‐mediated CH insertion in ClCH2CH2Cl follows the order methyl &gt; methine &gt; benzylic α‐CH bond on N‐substituents. The N,N‐dibutyl‐α‐diazo homologue 2c and Nα[α‐diazo‐α‐(diethylphosphono)acetyl]‐2‐methylindoline (2k) exclusively produced γ‐lactams 4c (67%) and 4k (81%) via insertion into the methylene β‐CH and methyl β‐CH bonds. tert‐Butyl N‐[α‐diazo‐α‐(dibenzylphosphono)acetyl]‐piperidine‐2‐carboxylate (2m) on similar treatment, followed by deprotection of the benzyl ester afforded the 7‐phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)‐catalyzed cyclization of N‐methyl‐N[4‐benzyloxy‐α‐(diethylphosphono)‐phenyl(diethyl‐phosphono)methyl]‐α‐diazo‐acetamide (2n) led to 1‐[4′‐benzylphenyl(diethylphosphono)methyl] ‐3‐(diethyl‐phosphono)azetidin‐2‐one (3n) in 78% yicld. The phosphono group at C‐7 of 3f was converted into the acetylamino group via a four‐step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b,c produced α‐phosphono‐β‐and γ‐lactams, 3b and 4c, in 6–24% ee and 25–29% ee, respectively.

Nature of nitrenium:carboxylate ion pair intermediates in the hydrolysis of O-aroyl-N-acetyl-N-(2,6-dimethylphenyl)hydroxylamines

O-Aroyl-N-acetyl-N-(2,6-dimethylphenyl)hydroxylamines [aroyl = benzoyl (1a), 3-nitrobenzoyl (1b), and pentafluorobenzoyl (1c)] are solvolysed in aqueous solutions by rate-limiting ionization to nitrenium : carboxylate ion pair intermediates. These in part collapse at the ortho position to give unstable 1,5-dimethyl-5-aroyloxy-6-acetyliminocyclohexa-l,3-dimes 2 that react further as described in the previous paper. The ion pairs from 1 also proceed directly to products of substitution para to the acetylamino group—4-aroyloxy-2,6-dimethylacetanilide 5, a product of internal return, and 4-hydroxy-2,6-dimethylacetanilide 6, a product of water addition. These same products also arise via ionization of 2. The ratio 5:6 obtained directly from 1 is significantly lower than that from 2, demonstrating that 1 and 2 do not ionize to exactly the same ion pairs. Experiments with 1a in the presence of bromide show that the yield of the cyclohexadiene is unaffected, while the yields of 5 and 6 are decreased, albeit to different amounts. Two new products, 4-bromo-2,6-dimethylacetanilide and 2,6-dimethylacetanilide, are observed in their places. Experiments with 1c in acid solutions demonstrate that the yield of cyclohexadiene can be decreased by H+, by protonation of the carboxylate ion in the ion pair. Using the H+ reaction as a clock, the lifetime of this ion pair, the initial ion pair in the ionization of 1, is calculated as ca. 10 ps. Thus this ion pair is too short-lived to react with external nucleophiles, and probably also with solvent. The trapping data for the p-ester 5 are shown to be inconsistent with a mechanism where a single ion pair serves as precursor, and this product is proposed to arise in part from a short-lived ion pair, and in part from a longer-lived one. The latter ion pair is probably also the species that gives rise to the p-phenol 6 by reaction with water. Using the bromide reaction as the clock, this ion pair is shown to have a lifetime of 0.25–0.50 ns. A number of mechanistic models incorporating these features are consistent with the experimental results, and two of these are discussed. Whatever the mechanism a minimum of three shortlived ion pair intermediates is required.

Bis(5-acetylamino-1,3,4-thiadiazole-2-sulfon)amide dihydrate

The molecules of the title compound [bis(5-acetylamino-1,3,4-thiadiazole-2-sulfonyl)amine dihydrate, C 8 H 9 N 7 O 6 S 4 .2H 2 O (1)] consist of two nearly planar acetylaminothiadiazolesulfonyl units which are parallel to one another. Coplanarity of the acetylamino groups and the thiadiazole rings is achieved by π-electron delocalization over these groups and by non-bonded S...O interactions [S1...O1 2.667 (4), S1'...O1' 2.661 (4) A]

Liquid chromatographic—atmospheric pressure chemical ionization mass spectral characterization of carboxylic acids and their glycine conjugates

A series of substituted benzoic acids and their glycine conjugates were characterized by liquid chromatography—atmospheric pressure chemical ionization mass spectrometry. Each substituted benzoic acid and its glycine conjugate were separated with a Cosmosil 5 C 8 column using three mobile phases. All negative-ion mass spectra of the substituted benzoic acids gave abundant [M  H] − and [M  COOH] − ions. For acids with halogen, nitro, cyano, and acetylamino groups, fragmentations corresponding to losses equivalent to the mass of each functional group were also observed. In addition, the alkoxyl group gave a characteristic fragmentation representing loss of the alkyl moiety. The abundances of the fragment ions due to the functional groups gave information on the position of the ring substituents. All of the positive- and negative-ion mass spectra of the glycine conjugates gave abundant [M + H] + and [M  H] − ions with characteristic fragment ions, respectively. Fragmentations of the glycine conjugates obtained in the positive-ion mode were different from those in the negative-ion mode. Similar information on the substituents was obtained for the glycine conjugates.

Random chemical modification of the oxygen-linked chloride-binding sites of hemoglobin: those in the central dyad axis may influence the transition between deoxy- and oxy-hemoglobin.

The features of random chemical modification are defined with reference to acetylation of bovine hemoglobin, which has been performed in a random manner so that all of the amino groups that participate in functional chloride binding (i.e., those that are oxygen-linked) could be identified. Random chemical modification, which has objectives different from those of both specific (selective) and extensive chemical modification, has been achieved for bovine hemoglobin with the mild reagent, 14C-methyl acetate phosphate; retention of function was demonstrated by a Hill coefficient of n = 2.2 for the modified hemoglobin. After removal of unmodified Hb chains, the mixture of randomly modified acetylated alpha or beta chains was subjected to tandem treatment with trypsin and chymotrypsin. Peptides were purified by HPLC and identified by amino acid analysis. The amount of radioactivity in the acetylated amino group of a purified peptide was taken as an estimate of the degree of chloride binding. For bovine Hb, two amino groups of the alpha-chain (Val-1 and Lys-99) and three amino groups of the beta-chain (Met-1, Lys-81, and Lys-103) were shown to be oxygen-linked (i.e., to have incorporated significantly more radioactivity in the deoxy conformation compared to the same site in the oxy conformation). Three of these sites were already known chloride-binding sites [i.e., Val-1(alpha), the N-terminus of the alpha-chain, and two sites between the 2 beta-chains of bovine hemoglobin, Met-1(beta) and Lys-81(beta); these findings support the conclusions of the random modification approach. Two other chloride-binding sites, Lys-99(alpha) and Lys-103(beta), align the sides of the central dyad axis connecting the two well-known major chloride-binding sites of bovine Hb. The interrelationship of these five chloride-binding sites was assessed by improved molecular graphics. When viewed through the central dyad axis, the functional chloride-binding sites in the central cavity appear to be symmetrically related and to connect the two major chloride-binding sites. Modifiers or mutants that are directed at these regions in the central dyad axis may favor the deoxy conformation to provide a lower oxygen affinity by preventing the constriction of the central cavity that normally occurs upon oxygenation.

Effects of site-specific acetylation on omega-conotoxin GVIA binding and function.

Chemical modification of omega-conotoxin GVIA (omega-CgTXGVIA) was performed using nonsaturating concentrations of acetic anhydride to generate seven distinct derivatives. Following separation of these peptides using reverse-phase HPLC (RP-HPLC), their individual molecular weights were determined using fast bombardment mass spectrometry (FAB-MS). Three peptides contained a single acetylated amino group, three possessed two acetylated amino groups, and the last contained three acetylations. For each peptide, the specific site of acetylation was confirmed using a scheme of tryptic digestion, under nonreducing conditions, followed by RP-HPLC and FAB-MS. Biological profiles for each peptide were obtained by analyzing their capacity to displace native 125I-omega-CgTx GVIA binding to rat hippocampal membranes and to block K(+)-stimulated 45Ca2+ influx into chick brain synaptosomes. The data indicate that successive additions of acetyl moieties to omega-CgTx GVIA lead to a loss of both binding affinity and Ca2+ influx inhibitory potency. Within the monoacetylated series, acetylation of the amino terminal of Cys-1, as compared to the epsilon-amino group of either Lys-2 or Lys-24, leads to the greatest shift in potency. In summary, these results indicate that basic (i.e., primary amino) groups, which are brought into close proximity as a result of disulfide bridging, are important in the functional blockade of neuronal Ca2+ channels by omega-CgTx GVIA.

Purification and characterization of a Fuc alpha 1–>2Gal beta 1–> and GalNAc beta 1–>-specific lectin in root tubers of Trichosanthes japonica.

A prominent lectin in the root tubers of Trichosanthes japonica was purified by affinity chromatography on a porcine stomach mucin-Sepharose column and termed TJA-II. The molecular mass of the native lectin was determined to be 64 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and TJA-II was separated into two different subunits of 33 and 29 kDa in the presence of 2-mercaptoethanol. The respective subunits contained mannose, N-acetylglucosamine, fucose, and xylose. It was determined by equilibrium dialysis to have two equal binding sites per molecule, the association constant toward tritium-labeled Fuc alpha 1-->2Gal beta 1-->3GlcNAc beta 1-->3Gal beta 1-->4GlcOT being K alpha = 3.05 x 10(5) M-1. The precise carbohydrate binding specificity of immobilized TJA-II was studied using various tritium-labeled oligosaccharides. A series of oligosaccharides possessing Fuc alpha 1-->2Gal beta 1--> or GalNAc beta 1--> groups at their nonreducing terminals showed stronger binding ability than ones with Gal beta 1-->GlcNAc (Glc) groups, indicating that TJA-II fundamentally recognizes a beta-galactosyl residue and the binding strength increases on substitution of the hydroxyl group at the C-2 position with a fucosyl or acetylamino group. This lectin column is useful for fractionating oligosaccharides or glycoproteins containing blood group type 1H, type 2H, and Sd antigenic determinants.

Two acetylamino derivatives of 2,4-bis(trichloromethyl)-1,3-benzdioxin showing different types of hydrogen bonding: (a) (C13C)CH?O=C and (b) N-H?O=C

8-Acetylamino-6-methyl-2,4-bis(trichloromethyl)-1,3-benzdioxin, (I), is monoclinic,P21/c,a=15.174(4),b=11.977(7),c=9.911(3)A,β=99.72(2)°. 6-Acetylamino-2,4-bis(trichloromethyl)-1,3-benzdioxin, (II), is monoclinic,P21/n,a=5.927(4),b=40.623(1),c =7.120(3)A,β=91.39(4)°. In compound (I) the imino hydrogen atom is locked in an intramolecular hydrogen bond to the proximate oxygen atom of the heterocyclic ring and is not available for intermolecular hydrogen bonding. Instead the weakly acidic hydrogen atom [Cl3C-C(2)]H takes part in a hydrogen bond to the carbonyl oxygen atom in another molecule. In compound (II) a “normal” intermolecular hydrogen bond of the type N-H⋯O=C occurs. The 6-acetylam-ino group is twisted about the (CAr-N) bond such that the angles N′H′⋯O=C, CArHAr⋯O=C, N′H′⋯O⋯HArCAr, at the carbonyl oxygen group total 360° (where N′H′ is in the related molecule). The packing in both compounds takes the form of infinite chains and in compound (II) partial overlap of the aromatic ring and the acetylamino group, with very little offset, also occurs.

Synthesis and pharmacological evaluation of 4,4a,5,6-tetrahydro-2H-thieno[2,3- h]cinnolin-3-ones bioisosters of antihypertensive and antithrombotic benzo[ h]cinnolinones

The 8-acetylamino-4,4a,5,6-tetrahydro-2H-thieno[2,3- h]cinnolin-3-one ( 2b) has been synthesized and tested for its pharmacological profile in comparison with the bioisoster 8-acetylamino-4,4a,5,6-tetrahydrobenzo( h)cinnolin-3(2H)one ( 1b), which we reported to be a potent antihypertensive and antithrombotic agent. The new compound retained antithrombotic properties which were higher than those of acetylsalycilic acid but without significant antihypertensive activity. Conformational analysis performed by molecular mechanic calculations suggests that the lack of activity could be due to a different orientation of the acetylamino group in the 2 compounds. In addition, the unsubstituted term 2a was found to be comparable to ASA as an antithrombotic agent.

Nitroacetyl Group as a Peptide Synthon: Synthesis of Dipeptides with an α,α‐Bisallylglycine Residue at the N‐Terminus

AbstractN‐Nitroacetyl derivatives of L‐proline, L‐valine, and L‐phenylalanine esters were prepared in two steps under mild conditions (Scheme 2). Regiospecific mono‐ and bis‐allylation of these nitroacetyl derivatives were accomplished in presence of a Pd(0) catalyst. The bis‐allyl derivatives 7–9 were obtained in 40–75% yield. The tertiary NO2 group in these compounds could be transformed into an acetylamino group by Zn/AcOH/Ac2O. The final products 11–13 are dipeptides in which the N‐terminal glycine residue bears two α‐allyl substituents.

Interaction of indomethacin with low molecular weight chitosan, and improvements of some pharmaceutical properties of indomethacin by low molecular weight chitosans

The interaction of four kinds of low molecular weight chitosans, which were different in molecular weight and degree of deacetylation, were studied in solution and the solid state using an anti-inflammatory drug, indomethacin (IM), as an acidic model molecule. The solubility of IM enhanced with increasing concentration of low molecular weight chitosan, especially C-I which had the lowest molecular weight and least degree of deacetylation. The C-I crystal complex was obtained in a molar ratio of 16:1 (IM: C-I) from aqueous solution. The data suggested that the acetyl group and amino group of chitosan played an important role in the complexation. The IM dissolution rates from kneaded mixtures with low molecular weight chitosans were enhanced in the order of C- I > C- II > C- III > C- IV (molecular weight: C- IV > C- III > C- II > C- I). The oral absorption rate of IM from C-I kneaded mixture was improved compared with IM alone.

Metabolic studies of explosives 6. Electron impact and chemical ionization mass spectrometry of metabolites of 2,4-dinitrotoluene.

A series of metabolites of 2,4-dinitrotoluene have been synthesized and analysed by electron impact and chemical ionization mass spectrometry. Identification characteristics of these metabolites by their mass spectra have been determined. Differentiation of isomers is made possible by electron impact ions which are characteristic to the position of the methyl group with regard to the nitro group and to the position of the carboxylic acid group with regard to the nitro group. Metabolites containing an acetyl amino group are characterized by an [M - COCH2]+. electron impact ion.

Separation of amino- and acetylamino-polycyclic aromatic hydrocarbons by reversed- and normal-phase high-performance liquid chromatography

In the field of chemical carcinogenesis, amino- and acetylamino-polycyclic aromatic hydrocarbons (PAHs) are among the most studied compounds. Many of these compounds have recently been detected in the environment. Presently, knowledge permitting predictions of the high-performance liquid chromatographic (HPLC) retention order of amino- and acetylamino-PAHs, particularly among their geometric isomers is lacking. In order to obtain a better understanding of the separation of these types of compounds, we have studied the separation of a series of structurally related amino- and acetylamino-PAHs derived from naphthalene, phenanthrene, anthracene, pyrene, benz[ a]anthracene, benzo[ a]pyrene, and benzo[ e]pyrene by using reversed-phase and normal-phase HPLC columns of different types (monomeric, polymeric, and chiral stationary phase). The results indicate: (i) Pirkle-type chiral stationary phase columns and the Zorbax SIL column can efficiently separate both the amino-PAHs and acetylamino-PAHs; (ii) in general, there was no correlation between retention time and molecular size; (iii) when acetylamino-PAHs were separated on the monomeric Zorbax ODS column, the isomer with the acetylamino group located at the carbon position of higher electron density has a shorter retention time; and (iv) separation of the parent PAHs was better than that of the amino-PAHs and acetylamino-PAHs. Our results thus may provide useful information for the analysis of amino-PAHs, particularly for distinguishing the geometric isomers of environmental samples.

Naphthoquinone methide type near-i.r. dye: the properties and structure of 4-(2′-acetylamino-4′-diethylaminophenylimino)-1,4-dihydronaphthylidene- malononitrile

The introduction of an acetylamino group at the 2′-position in the aniline ring of a naphthoquinone methide dye produced a red shift with a large increase in the molecular extinction coefficient in CHCI3 solution, and an intramolecular ring-closure reaction of the compound under alkaline conditions gave a new blue dye; the stereochemistry of this chromophoric system was determined by X-ray analysis.

Highly phosphorylated derivatives of chitin, partially deacetylated chitin and chitosan as new functional polymers: metal binding property of the insolubilized materials

Highly phosphorylated derivatives of chitin and deacetylated chitins (DA-chitins) were insolubilized by the cross-linking reaction with adipoyl chloride in methanesulphonic acid, and their metal binding ability to Mg 2+, Ca +, Sr 2+, Ba 2+, Mn 2+, Ni 2+, Cu 2+, Zn 2+ and Cd 2+ was investigated. Generally alkaline-earth metals and Mn 2+ were adsorbed strongly to these derivatives than to original chitin or DA-chitins, while the transition elements except Mn 2+ were adsorbed strongly to DA-chitins than to these derivatives. The pH dependence for the Ca 2+-adsorption to these materials showed that the amount of adsorbed Ca 2+ increased with a rise in pH, suggesting the large contribution of phosphoryl group. However, the differential i.r. spectra of chitin phosphate or DA-chitin phosphate between presence and absence of Ca 2+ suggested that not only the phosphoryl group but also other groups such as hydroxyl group and also acetylamino group concerned cooperatively to the metal binding. Results on the potentiometric titration for these cross-linked derivatives were also discussed comparing with those for non-cross-linked phosphorylated derivatives.

Relationship between paracetamol binding to and its oxidation by two cytochromes P-450 isozymes--a proton nuclear magnetic resonance and spectrophotometric study.

From the hepatic cytochrome P-450 isozymes b and c isolated from rats treated with phenobarbital and 3-methylcholanthrene respectively, only cytochrome P-450c was found to be active in the oxidation of paracetamol, in the presence of glutathione ultimately leading to the formation of the 3-glutathionyl conjugate. Paracetamol interacted with both cytochrome P-450b and c, as shown by difference spectrophotometry. Cytochrome P-450b was found to have a higher affinity for paracetamol than cytochrome P-450c and demonstrated a type I spectral change, whereas in the case of cytochrome P-450c a reverse type I spectral change was observed. Proton n.m.r. longitudinal relaxation rate measurements revealed that in the case of cytochrome P-450c, paracetamol was orientated with its phenolic hydroxyl group in closest proximity to the central haem iron ion. In the case of cytochrome P-450b, the acetylamino group of paracetamol most closely approached the haem iron ion.