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PubMed1996

Determination of 4,4'-methylene-bis(2-chloroaniline)-DNA adduct formation in rat liver and human uroepithelial cells by the 32P postlabeling assay.

The probable human carcinogen 4,4'-methylene-bis(2-chloroaniline) (MOCA) was utilized to develop biomarkers of exposure to occupational carcinogens. The 32P postlabeling assay, utilizing the nuclease P1 enhancement procedure, was used to evaluate MOCA-DNA adduct formation in target tissues. Male Sprague-Dawley rats were treated with different dosing regimens of MOCA, and DNA was isolated from the liver. Additionally, a human uroepithelial cell (HUC) line was treated with N-hydroxy-MOCA for 24 hr, cells were harvested, and DNA was isolated. DNA was analyzed for MOCA-DNA adduct formation by the 32P postlabeling assay. Five MOCA adducts were detected in rat liver DNA. Adduct A, which corresponded to N-(deoxyadenosin-8-yl)-4-amino-3-chlorobenzyl alcohol, was the major adduct in rat liver DNA appearing in all treatment groups. Levels of adduct A were higher when MOCA was administered by ip injection versus oral gavage. Phenobarbital pretreatment increased the amount of adduct A approximately 12-fold. The pathway leading to the formation of adduct A in DNA from HUC appeared to be saturated at the concentrations used: 2.5, 5, and 10 microM. However, an additional adduct (E) was observed at the 10 microM treatment level only. A major DNA adduct was detected in the target tissue of rats and target human cells for MOCA-induced carcinogenesis, thus making it useful as a biomarker of exposure. Other DNA adducts were also observed with the different doses and routes of exposure investigated.

Animals↗

PubMed2006

Manganese-oxide-coated alumina: a promising sorbent for defluoridation of water.

In this study, adsorption potential of a new sorbent manganese-oxide-coated alumina (MOCA) was investigated for defluoridation of drinking water using batch and continuous mode experiments. The effects of different parameters such as pH, initial fluoride concentration and co-existing ions (usually present in groundwater sample) were studied to understand the adsorption behavior of the sorbent under various conditions. Optimum removal of fluoride ions occurred in a pH range of 4-7. Results of the present study indicate that fluoride adsorption rate and adsorption capacity of MOCA are far superior to that of activated alumina (AA), which was used as the base material for MOCA preparation. The MOCA can be effectively regenerated using 2.5% NaOH as eluent. The Langmuir equilibrium model was found to be suitable for describing the fluoride sorption on AA and MOCA. The maximum fluoride uptake capacity for MOCA and AA was found to be 2.85 and 1.08 mg g(-1), respectively. The kinetic results showed that the fluoride sorption to MOCA followed pseudo--second-order kinetics with a correlation coefficient greater than 0.98. The fluoride sorption capacity at breakthrough point for both the adsorbents was greatly influenced by bed depth. A bed depth service time (BDST) approach was adopted to describe the continuous flow system. The batch and column studies demonstrated the superiority of MOCA over AA in removing fluoride from the drinking water system.

Adsorption↗

PubMed1992

Contributions of human liver cytochrome P450 enzymes to the N-oxidation of 4,4'-methylene-bis(2-chloroaniline).

4,4'-Methylene-bis(2-chloroaniline) (MOCA) can produce tumors in rodents and dogs and an increased incidence of bladder tumors has been reported in exposed workers. It is therefore of interest to identify the human cytochrome P450 (P450) enzymes involved in MOCA N-oxidation, the primary reaction involved in the formation of an electrophilic product. Human liver microsomes were fractionated and MOCA N-oxidation activity was monitored through the procedure. The most active enzyme fraction corresponded to P450 3A4, as determined by immunochemical assays and N-terminal amino acid sequence analysis. Yeast recombinant P450 3A4 also had MOCA N-oxidation activity. Purified human liver P450 2A6 showed catalytic activity; however, anti-P450 2A6 inhibited less than 20% of the microsomal activity while anti-P450 3A4 inhibited up to 75%. Levels of marker activities of both P450 3A4 (nifedipine oxidation) and P450 2A6 (coumarin 7-hydroxylation) were measured in a set of human liver microsomes and both were correlated with MOCA N-oxidation rates. Gestodene and troleandomycin inhibited up to half of the microsomal MOCA N-hydroxylation activity but 7,8-benzoflavone showed only slight inhibition. Anti-P450 3A4 inhibited (up to 80% of) the microsomal transformation of MOCA to a product genotoxic as judged by bacterial SOS response. The work indicates that P450 3A4 makes a major contribution to human liver microsomal MOCA N-oxidation, and P450 2A6 has a minor role. P450 1A2, which catalyzes the hydroxylation of many arylamines, does not contribute to a great extent.

Benzoflavones↗

PubMed2005

Modifier of cell adhesion regulates N-cadherin-mediated cell-cell adhesion and neurite outgrowth.

Modifier of cell adhesion (MOCA) is a member of the dedicator of cytokinesis 180 family of proteins and is highly expressed in CNS neurons. MOCA is associated with Alzheimer's disease tangles and regulates the accumulation of amyloid precursor protein and beta-amyloid. Here, we report that MOCA modulates cell-cell adhesion and morphology. MOCA increases the accumulation of adherens junction proteins, including N-cadherin and beta-catenin, whereas reducing endogenous MOCA expression lowers cell-cell aggregation and N-cadherin expression. MOCA colocalizes with N-cadherin and actin in areas of cell-cell and cell substratum contact and is expressed in neuronal processes. MOCA accumulates during neuronal differentiation, and its expression enhances NGF-induced neurite outgrowth and morphological complexity. We conclude that MOCA regulates N-cadherin-mediated cell-cell adhesion and neurite outgrowth.

Animals↗

PubMed2026

Comparing the Efficacy of Mechanochemical Ablation Versus Radiofrequency Ablation for Treating Great Saphenous Vein Incompetence: A Meta-Analysis.

BACKGROUND: The objective of this meta-analysis was to compare the efficacy of mechanochemical ablation (MOCA) and radiofrequency ablation (RFA) in the treatment of great saphenous vein (GSV) incompetence. METHODS: Online databases including PubMed, Cochrane Library, Embase, and Web of Science were searched to collect randomized controlled trials (RCTs) and cohort studies comparing MOCA and RFA in the treatment of varicose veins in lower extremities from database inception to October 2025. Primary outcome was anatomic success. Secondary outcomes were visual analog scale (VAS), Aberdeen Varicose Vein Questionnaire score (AVVQ), and complications. Two reviewers independently screened the retrieved literature, extracted data, and assessed the risk of bias in the included studies. Subsequent analysis was performed using RevMan 5.3. RESULTS: A total of four RCTs, one cohort study and retrospective cross-sectional study involving 737 patients (380 MOCA patients and 357 RFA patients) were included. The meta-analysis results showed that the RFA group was significantly better than the MOCA group in short term and long term of anatomical success rate [(odds ratio [OR] = 0.38; 95% confidence interval [CI] (0.20, 0.71), P = 0.003), (OR = 0.17, 95% CI (0.06, 0.45), P = 0.0003)], but patients in the MOCA group had significantly lower perioperative period pain (mean difference [MD] = -4.48, 95% CI (-7.58, -1.37), P = 0.005] and required fewer days to return to normal activities (MD = -0.76, 95% CI, (-0.95, -0.57), P < 0.001). No significant differences were observed between the two groups in minor and major complications [(OR = 0.93, 95% CI (0.66, 1.33), P = 0.70), (OR = 1.30, 95% CI (0.32, 5.28), P = 0.72)] or quality of life scores (MD = -0.45, 95% CI (-2.53 to 1.63), P = 0.67). CONCLUSION: MOCA of GSV incompetence is an effective and safe method. Compared with RFA, it has lower postoperative pain score and faster recovery time. However, the anatomical success rates were significantly lower with MOCA than with RFA. Therefore, long-term follow-up to evaluate the impact on clinical results is required.

Humans↗

PubMed1989

Covalent binding of 4,4'-methylenebis-(2-chloroaniline) to rat liver DNA in vivo and of its N-hydroxylated derivative to DNA in vitro.

The binding of [ring-3H]4,4'-methylenebis(2-chloroaniline) (MOCA) to rat liver DNA following i.p. injection is demonstrated. Three discrete adducts were eluted on HPLC following enzymic hydrolysis to the nucleoside level. Three adducts, with the same retention times on HPLC, were present after i.p. injection of the N-acetyl derivative of MOCA tritiated in the benzene rings. Only two of these adducts were found when the N-acetyl derivative, tritiated on the acetyl group, was used. Thus, at least one of the adducts formed by MOCA is not acetylated. The N-hydroxy derivative of MOCA was synthesised and reacted with DNA in vitro. Following enzymic hydrolysis of this DNA, the major product was shown to co-elute with the radiolabelled non-acetylated adduct produced in the liver DNA of animals injected with [ring-3H]MOCA. This same compound was also isolated following the reaction of N-hydroxy-4-amino-3-chlorobenzyl alcohol with DNA, and subsequent enzymic hydrolysis. The NMR and mass spectra of the synthetic adduct were consistent with N-(deoxyadenosin-8-yl)-4-amino-3-chlorobenzyl alcohol. Thus, the major adduct formed in vivo has involved cleavage of the bond between the methylene bridge and one of the aromatic nuclei of MOCA.

Acetylation↗

PubMed1975

Determination of 3,3'-dichloro-4,4'-diaminodiphenylmethane in air.

A simple gas chromatographic method is described for the analysis of 3,3'-dichloro-4,4'diaminodiphenylmethane (MOCA) in air. MOCA is quantitatively collected on a Gas-Chrom S tube and the solid sorbent is extracted with acetone. An aliquot sample of the extract is introduced directly into the gas chromatograph, using a microsyringe and the sample is chromatographed on a 1-ft.,silylated 10% Dexsil column. The peak area of MOCA is measured and related to the concentration via a calibration curve prepared with a constant volume of standards. The chloroanilines associated with MOCA cause no interference; however, interference can be expected from any compounds having a retention time identical to that of MOCA. As little as 0.002 mug of MOCA per mul of acetone can be detected by this method.

Absorption↗

PubMed1989

Metabolic oxidation of the carcinogens 4-aminobiphenyl and 4,4'-methylene-bis(2-chloroaniline) by human hepatic microsomes and by purified rat hepatic cytochrome P-450 monooxygenases.

Metabolic N-oxidation and ring-oxidation of carcinogenic arylamines by hepatic cytochromes P-450 are generally regarded as critical activation and detoxification pathways, respectively. Two arylamines with known human exposure, 4-aminobiphenyl (ABP) and 4,4'-methylene-bis(2-chloroaniline) (MOCA), have been examined as substrates for 10 different purified rat hepatic cytochromes P-450 and for human liver microsomal preparations from 22 individuals. Metabolites were analyzed by high-performance liquid chromatography and flow scintillation techniques. As reported for certain other carcinogenic arylamines, the isosafrole-inducible isozyme, P-450ISF-G, had the highest catalytic activity for ABP N-oxidation (13.6 nmol/min/nmol P-450), but P-450BNF-B, P-450UT-A, P-450UT-F, and P-450PB-B also showed appreciable activity. Ring-oxidation of ABP occurred only to a minor extent. In contrast, N-oxidation of MOCA was preferentially catalyzed by the phenobarbital-inducible enzymes, P-450PB-B and P-450PB-D (9.0 and 6.6 nmol/min/nmol P-450, respectively). MOCA ring-oxidation and methylene carbon oxidation showed varied cytochrome P-450 selectivity and accounted for 14 to 79% of total oxidation products. There was a 44-fold variation in rates of ABP N-oxidation in the 22 human liver microsomal preparations, while rates of N-oxidation of MOCA varied only 8-fold. Ring/methylene carbon-oxidation of MOCA accounted for 6-19% of total oxidation products in the case of the human microsomal preparations, whereas ring-oxidation of ABP accounted for less than 7% of total oxidation. In addition, there was a strong correlation (R = 0.90) between rates of ABP N-oxidation and phenacetin O-deethylation, which is considered a human genetic polymorphism. Moreover, both the ABP N-oxidation and phenacetin O-deethylation activities of human liver microsomes showed a good correlation (R = 0.72) with the levels of cytochrome P-450 immunochemically related to rat P-450ISF-G. These data indicate that specific inducible and constitutive cytochromes P-450 are involved in the metabolic activation and detoxification of the carcinogens ABP and MOCA. Therefore, individual profiles of cytochromes P-450, affected by both environmental and genetic factors, may be significant determinants of individual susceptibility to arylamine carcinogenesis.

Aminobiphenyl Compounds↗

PubMed1996

Gas chromatographic determination and negative-ion chemical ionization mass spectrometric confirmation of 4,4'-methylenebis(2-chloroaniline) in urine via thin-layer chromatographic separation.

An analytical method for monitoring 4,4'-methylenebis(2-chloroaniline) (MOCA) in urine was developed. The MOCA extract from a urine sample was derivatized with pentafluoropropionic anhydride and subsequently cleaned-up via TLC before being analysed by a gas chromatograph equipped with an electron capture detector. Heptafluorobutyric anhydride derivatized MOCA was used as the internal standard during quantification. The method showed that the analytical interferences are effectively minimized by using the TLC technique for sample clean-up. Recoveries of spiked MOCA in urine at levels of 7.5, 22 and 62.5 micrograms dm-3 were all over 90% with the limit of detection determined to be 1 microgram dm-3. Confirmation of MOCA in a urine sample was performed by using a gas chromatograph mass spectrometer in negative-ion chemical ionization mode.

Chromatography, Thin Layer↗

PubMed2004

The human nuclear SRcyp is a cell cycle-regulated cyclophilin.

Cyclophilins of the Moca family (Cavarec, L., Kamphausen, T., Dubourg, B., Callebaut, I., Lemeunier, F., Metivier, D., Feunteun, J., Fischer, G., and Modjtahedi, N. (2002) J. Biol. Chem. 277, 41171-41182) are found only in organisms of the animal kingdom and share several structural and enzymatic features. The presence of serine/arginine (S/R) dipeptide repeats in their C-terminal tail suggests that these enzymes belong to the SR protein family involved in the regulation of gene expression. The function of this group of cyclophilins is currently unknown. However, their C-terminal tails contain a highly conserved polypeptide signature segment (the moca domain), which may well be involved in the functional regulation of these proteins. We report here the identification of five Cdc2-type phosphorylation sites gathered in and around the moca domain of SRcyp, a human cyclophilin belonging to the Moca family. The segment of SRcyp containing the identified sites is specifically phosphorylated in mitotic cells. This mitosis-specific phosphorylation was inhibited by treatment of the cells with roscovitine, a specific inhibitor of cyclin-dependent kinases, suggesting that the unknown activity of the moca domain of SRcyp requires mitotic regulation by the Cdc2-cyclin B kinase complex. The Cdc2-cyclin B complex was found to phosphorylate four of the five identified phosphorylation sites in vitro, providing further support for this possibility. Like many factors stored in nuclear speckles and involved in the regulation of gene expression, this nuclear cyclophilin displays a predominantly diffuse cytoplasmic distribution at the onset of mitosis. Only in late telophase is SRcyp recruited to the newly formed nuclei. The transit of SRcyp through mitotic interchromatin granule clusters, before re-entering the nucleus, suggests that the timing of the appearance of this cyclophilin in the telophasic nuclei is tightly coordinated with post-mitotic events. Human SRcyp is the first cell cycle-regulated cyclophilin to be described.

Amino Acid Sequence↗

PubMed1993

Monitoring exposure to 4,4'-methylene-bis(2-chloroaniline) through the gas chromatography-mass spectrometry measurement of adducts to hemoglobin.

4,4'-Methylene-bis(2-chloroaniline) (MOCA) is widely used as a curing agent in the plastics industry. The determination of the covalently bound reaction products to hemoglobin (Hb) has been investigated as a biomonitoring method for occupational exposure to this potential human carcinogen. Initial studies using the 14C-ring-labeled MOCA showed that 24 hr after a single IP dosage to rats (3.74 mumole/kg), 0.08% of the administered dose was adducted to the Hb, and base hydrolysis liberated 38% of the bound radioactivity. The only product released on hydrolysis was the parent diamine. A specific and sensitive assay procedure using capillary gas chromatography-mass spectrometry has been developed for determining the base-released MOCA adduct down to levels of 20 pmole/g Hb. This method has been used to establish a linear dose-response relationship in IP dosed rats between production of the adduct and dose of MOCA (3.74-44.94 mumole/kg). It is proposed to use analysis of the Hb adduct as a dosimeter for industrial workers exposed to MOCA.

Animals↗

PubMed2026

Blood mitochondrial heteroplasmic variants and cognitive performance in late midlife: REGARDS study.

BACKGROUND: Studies linking mitochondrial DNA (mtDNA) variants to cognition yielded inconsistent findings, and the underlying mechanisms remain unclear. We investigated whether mtDNA heteroplasmic variants were associated with cognitive outcomes, including the Montreal Cognitive Assessment (MoCA), in 197 late midlife adults from the Reasons for Geographic and Racial Differences in Stroke (REGARDS) cohort with complete data. METHODS: MtDNA was sequenced from blood using targeted deep sequencing. Adjusted linear and mixed-effects models examined the associations by functional regions, genes, total variant burden, nonsynonymous variants, and control regions. RESULTS: Heteroplasmic variants in the control region (β = -0.44, 95% CI: -0.83, -0.05, p = 0.027) and transfer RNA (tRNA) genes (β = -1.34, 95% CI: -2.58, -0.11, p = 0.034) were associated with MoCA baseline scores. Individual variants in cytochrome c oxidase subunit 1 (CO1) (β = -1.51, 95% CI: -2.54, -0.47, p = 0.005), NADH dehydrogenase subunit 1 (ND1) (β = -2.63, 95% CI: -4.56, -0.70, p = 0.008), and Displacement Loop (D-LOOP2) (β = -2.25, 95% CI: -4.20, -0.30, p = 0.025) was associated with reduced baseline MoCA scores. The ND6 (β = −1.23, 95% CI: −2.09, − 0.37, p = 0.006), ND4 (β = −1.11, 95% CI: −2.02, − 0.20, p = 0.018), ATP Synthase Membrane Subunit 8 (ATP8; β = −1.38, 95% CI: −2.63, − 0.13, p = 0.031), and D-LOOP1 (β = −0.61, 95% CI: −1.20, − 0.01, p = 0.045) genes suggested a potential association with executive function. Longitudinal Animal Fluency Test (AFT) scores were inversely associated with heteroplasmic variants in coding regions (β = -0.10, 95% CI: -0.19, -0.006, p = 0.049), the total number of variants (β = -0.06, 95% CI: -0.11, -0.003, p = 0.037) and total nonsynonymous variants (β = -0.11, 95% CI: -0.21, -0.01, p = 0.040). Variants in the control region were associated with the greatest decline in verbal fluency (β = −0.20, 95% CI: −0.39 to − 0.002, p = 0.049). No associations were observed between mitochondrial variants and verbal memory performance or the MoCA composite scores. CONCLUSIONS: Our study indicates that mitochondrial variants measured in blood may provide insight into cognitive function during midlife. However, additional studies are needed to validate these associations and to address potential power limitations in our study.

Humans↗

PubMed1990

Review of the genotoxicity and carcinogenicity of 4,4'-methylene-dianiline and 4,4'-methylene-bis-2-chloroaniline.

4,4'-Methylene-dianiline (MDA) and 4,4'-methylene-bis-2-chloroaniline (MOCA) are polycyclic aromatic amines that are currently used in industry. Both compounds have been found to be bacterial mutagens and to be positive in a number of assays for genotoxicity. In animal studies, MDA has induced thyroid and liver neoplasms while exposure to MOCA resulted in a variety of tumors including those of the liver, mammary gland and bladder. Epidemiologic proof of human carcinogenicity of both compounds is lacking; however, there is evidence that MOCA can be metabolized to mutagenic products by human tissue. In this paper, the major finding concerning the biotransformation, genotoxicity and carcinogenicity of MDA and MOCA are reviewed.

Aniline Compounds↗

PubMed1992

Induction of ornithine decarboxylase activity by 4,4'-methylene bis(2-chloroaniline) in the rat.

The effects of the curative extender 4,4'-methylene bis (2-chloraniline) (MOCA), an established experimental carcinogen that exhibits activity in rat liver, on hepatic ornithine decarboxylase (ODC) activity was investigated. Male Sprague-Dawley rats were injected i.p. with 75 mg/kg MOCA and killed 6, 12, 18, 24, 42 and 48 h later. Stimulation with MOCA of liver cytosolic ODC was first evident at 6 h, peaked at 12 h and returned to control levels by 42 h. The liver enzyme was refractory to stimulation by a second treatment of MOCA within the dosing intervals examined. The magnitude of stimulation of the enzyme by this aromatic amine was dependent on dose and route of administration.

Animals↗

PubMed2000

Atomic force microscopy and electron microscopy analysis of retrovirus Gag proteins assembled in vitro on lipid bilayers.

We have used an in vitro system that mimics the assembly of immature Moloney murine leukemia virus (M-MuLV) particles to examine how viral structural (Gag) proteins oligomerize at membrane interfaces. Ordered arrays of histidine-tagged Moloney capsid protein (his-MoCA) were obtained on membrane bilayers composed of phosphatidylcholine (PC) and the nickel-chelating lipid 1, 2-di-O-hexadecyl-sn-glycero-3-(1'-2"-R-hydroxy-3'N-(5-amino-1-carboxy pentyl)iminodiacetic acid)propyl ether (DHGN). The membrane-bound arrays were analyzed by electron microscopy (EM) and atomic force microscopy (AFM). Two-dimensional projection images obtained by EM showed that bilayer-bound his-MoCA proteins formed cages surrounding different types of protein-free cage holes with similar cage holes spaced at 81.5-A distances and distances between dissimilar cage holes of 45.5 A. AFM images, showing topological features viewed near the membrane-proximal domain of the his-MoCA protein, revealed a cage network of only symmetrical hexamers spaced at 79-A distances. These results are consistent with a model in which dimers constitute structural building blocks and where membrane-proximal and distal his-MoCA regions interact with different partners in membrane-bound arrays.

Capsid↗

PubMed1998

Hemoglobin binding of bicyclic aromatic amines.

Aromatic diamino compounds, e.g., 4,4'-methylenebis(2-chloroaniline) (MOCA) and 4,4'-methylenedianiline (MDA), are used as curing agents in the production of elastomers. Since MOCA and MDA are mutagenic and carcinogenic, substitutes are of great commercial interest. For benzidine it has been shown that ortho substitution with methyl groups yields the nonmutagenic 3,3',5,5'-tetramethylbenzidine. Therefore, MDA analogues with large substituents in the ortho position have been synthesized. The substituents are supposed to inhibit the formation of the N-hydroxyarylamines which are the putative genotoxic intermediates. We investigated the biological availability of the N-hydroxylamines of ortho-substituted diamines and of known carcinogenic diamines in female Wistar rats, by determining hemoglobin (Hb) adducts. Hb from rats dosed with 0.5 mmol/kg diamine and from controls was isolated and hydrolyzed in base. The released diamine and monoacetyldiamine were quantified by HPLC with electrochemical detection and/or GC/MS. MDA, 4,4'-oxydianiline (ODA), 4,4'-ethylenedianiline, and 4,4'-thiodianiline (TDA) bound to hemoglobin as diamine and as monoacetyl-diamine. 4,4'-Methylenebis(2,6-dimethylaniline), 4,4'-methylenebis(2,6-diethylaniline), MOCA, and 4,4'-sulfonyldianiline (dapsone) bound only as diamine to Hb. 4,4'-Methylenebis(2,6-dichloroaniline) did not bind to Hb. Thus, the presence of two substituents in the ortho position and the presence of electron-withdrawing groups in the para position to the amino group drastically reduced the formation of Hb adducts. The amount of hemoglobin adducts was compared to their carcinogenic potency. The extent of hemoglobin binding of the bicyclic diamines (dapsone, 3,3'-dichlorobenzidine, MDA, MOCA, TDA, ODA, and benzidine) increases with their carcinogenic potency.

Amines↗

PubMed1992

Characterization of 4,4'-methylenebis(2-chloroaniline)--DNA adducts formed in vivo and in vitro.

4,4'-Methylenebis(2-chloroaniline) (MOCA) is a genotoxic and carcinogenic industrial chemical to which there is considerable potential human exposure. Since metabolic activation and formation of DNA adducts are believed to be important for the induction of these effects, DNA was treated in vitro with radiolabeled N-hydroxy-MOCA, the presumed proximate carcinogenic metabolite formed in vivo. Two major radioactive peaks were observed after HPLC separation of enzymatic hydrolysates. The two products were analyzed by MS and characterized as N-(deoxyadenosine-8-yl)-4-amino-3-chlorobenzyl alcohol and N-(deoxyadenosin-8-yl)-4-amino-3-chlorotoluene. The same adducts were also the major adducts formed in DNA of tissues from rats treated with radiolabeled MOCA. They were eliminated from rat liver with non-linear kinetics, in agreement with observations made for other carcinogens. The selective reaction of N-hydroxy-MOCA with DNA-adenine and the formation of single arylamine ring adducts suggest a substitution mechanism involving an intermediate with strong SN1 character, aided by the negative inductive effect of the ortho-chlorine. Due to tautomer formation, the initial adduct may be inherently unstable and undergo cleavage at the 1'-carbon-methylene bond to yield the observed adducts.

Animals↗

PubMed1997

Structural analysis of membrane-bound retrovirus capsid proteins.

We have developed a system for analysis of histidine-tagged (His-tagged) retrovirus core (Gag) proteins, assembled in vitro on lipid monolayers consisting of egg phosphatidylcholine (PC) plus the novel lipid DHGN. DHGN was shown to chelate nickel by atomic absorption spectrometry, and DHGN-containing monolayers specifically bound gold conjugates of His-tagged proteins. Using PC + DHGN monolayers, we examined membrane-bound arrays of an N-terminal His-tagged Moloney murine leukemia virus (M-MuLV) capsid (CA) protein, His-MoCA, and in vivo studies suggest that in vitro-derived His-MoCA arrays reflect some of the Gag protein interactions which occur in assembling virus particles. The His-MoCA proteins formed extensive two-dimensional (2D) protein crystals, with reflections out to 9.5 A resolution. The image-analyzed 2D projection of His-MoCA arrays revealed a distinct cage-like network. The asymmetry of the individual building blocks of the network led to the formation of two types of hexamer rings, surrounding protein-free cage holes. These results predict that Gag hexamers constitute a retrovirus core substructure, and that cage hole sizes define an exclusion limit for entry of retrovirus envelope proteins, or other plasma membrane proteins, into virus particles. We believe that the 2D crystallization method will permit the detailed analysis of retroviral Gag proteins and other His-tagged proteins.

Amino Acid Sequence↗