Development of acetaminophen proline prodrug

In this research work, proline ester prodrug of acetaminophen (Pro-APAP) was synthesized and evaluated for its stability in PBS buffer at various pH and Caco-2 cell homogenate. The Pro-APAP is more stable at lower pH than higher pH, with half-life of 120 min in PBS buffer at pH 2.0, half-life of 65 min at pH 5.0, and half life of 3.5 min at pH 7.4, respectively. The half-life of Pro-APAP in Caco-2 cell homogenate is about 1 min, much shorter than the half-life in PBS buffer at pH 7.4, indicating enzymes in the cell homogenate contribute to the hydrolysis of the ester bond. Carboxypeptidase A was incubated with Pro-APAP at pH 7.4 with half-life of 3.8 min which is very close to the half life in buffer itself. This clearly indicates carboxypeptidase A is not one of the enzymes contributing to the hydrolysis of the prodrug. Physicochemical characteristics such as melting point and stability of newly synthesized prodrug were determined by MDSC technique.     

Organization of the multiple coenzymes and subunits and role of the covalent flavin link in the complex heterotetrameric sarcosine oxidase

Heterotetrameric (alphabetagammadelta) sarcosine oxidase from Corynebacterium sp. P-1 (cTSOX) contains noncovalently bound FAD and NAD(+) and covalently bound FMN, attached to beta(His173). The beta(His173Asn) mutant is expressed as a catalytically inactive, labile heterotetramer. The beta and delta subunits are lost during mutant enzyme purification, which yields a stable alphagamma complex. Addition of stabilizing agents prevents loss of the delta but not the beta subunit. The covalent flavin link is clearly a critical structural element and essential for TSOX activity or preventing FMN loss. The alpha subunit was expressed by itself and purified by affinity chromatography. The alpha and beta subunits each contain an NH(2)-terminal ADP-binding motif that could serve as part of the binding site for NAD(+) or FAD. The alpha subunit and the alphagamma complex were each found to contain 1 mol of NAD(+) but no FAD. Since NAD(+) binds to alpha, FAD probably binds to beta. The latter could not be directly demonstrated since it was not possible to express beta by itself. However, FAD in TSOX from Pseudomonas maltophilia (pTSOX) exhibits properties similar to those observed for the covalently bound FAD in monomeric sarcosine oxidase and N-methyltryptophan oxidase, enzymes that exhibit sequence homology with beta. A highly conserved glycine in the ADP-binding motif of the alpha(Gly139) or beta(Gly30) subunit was mutated in an attempt to generate NAD(+)- or FAD-free cTSOX, respectively. The alpha(Gly139Ala) mutant is expressed only at low temperature (t(optimum) = 15 degrees C), but the purified enzyme exhibited properties indistinguishable from the wild-type enzyme. The much larger barrier to NAD(+) binding in the case of the alpha(Gly139Val) mutant could not be overcome even by growth at 3 degrees C, suggesting that NAD(+) binding is required for TSOX expression. The beta(Gly30Ala) mutant exhibited subunit expression levels similar to those of the wild-type enzyme, but the mutation blocked subunit assembly and covalent attachment of FMN, suggesting that both processes require a conformational change in beta that is induced upon FAD binding. About half of the covalent FMN in recombinant preparations of cTSOX or pTSOX is present as a reversible covalent 4a-adduct with a cysteine residue. Adduct formation is not prevented by mutating any of the three cysteine residues in the beta subunit of cTSOX to Ser or Ala. Since FMN is attached via its 8-methyl group to the beta subunit, the FMN ring must be located at the interface between beta and another subunit that contains the reactive cysteine residue.     

Comparative pulmonary toxicity of cadmium and nickel: histopathological and bronchoalveolar lavage analysis

Pulmonary toxicity of cadmium and nickel was evaluated in rat lungs following intratracheal instillation of their chlorides. Concentration of both the metals varied from 0.2-5 mM. Both the metals increased total number of cells, number of polymorphonuclear neutrophils, total protein, sialic acid and the activity of lactate dehydrogenase and beta-glucuronidase in bronchoalveolar lavage 3 days after exposure. Increase in the levels of the selected parameters was more following Cd exposure than in Ni exposed rats. Histologically there was an inflammatory response and interstitial fibroblastic proliferation in the lungs of Cd exposed animals. These changes were mild in Ni-exposed animals and higher concentrations of Ni were needed to produce changes similar to those produced by smaller concentrations of Cd.     

EBV structural antigens, gp350 and gp85, as targets for ex vivo virus-specific CTL during acute infectious mononucleosis: potential use of gp350/gp85 CTL epitopes for vaccine design

For many years, EBV vaccine development efforts have concentrated on the use of structural Ag, gp350, and have been directed toward Ab-mediated blocking virus attachment to the target cell. There is increasing evidence to suggest that the development of neutralizing Abs in vaccinated animals does not always correlate with protection; nevertheless, it has been postulated that gp350-specific T cell-mediated immune responses may have an effector role in protection. This hypothesis has largely remained untested. In the present study, we demonstrate that CTL from acute infectious mononucleosis patients display strong ex vivo reactivity against the EBV structural Ags, gp85 and gp350. Moreover, long-term follow up studies on infectious mononucleosis-recovered individuals showed that these individuals maintain gp350- and gp85-specific memory CTL, albeit at low levels, in the peripheral blood. These results strongly suggest that CTL specific for EBV structural proteins may play an important role in the control of EBV infection during acute infection. More importantly, we also show that prior immunization of HLA A2/Kb transgenic mice with gp350 and gp85 CTL epitopes induced a strong epitope-specific CTL response and afforded protection against gp85- or gp350-expressing vaccinia virus challenge. These results have important implications for future EBV vaccine design and provides evidence, for the first time, that CTL epitopes from EBV structural proteins may be used for establishing strong antiviral immunity against EBV infection.     

Structure of the flavocoenzyme of two homologous amine oxidases: monomeric sarcosine oxidase and N-methyltryptophan oxidase

Monomeric sarcosine oxidase (MSOX) and N-methyltryptophan oxidase (MTOX) are homologous enzymes that catalyze the oxidative demethylation of sarcosine (N-methylglycine) and N-methyl-L-tryptophan, respectively. MSOX is induced in various bacteria upon growth on sarcosine. MTOX is an E. coli enzyme of unknown metabolic function. Both enzymes contain covalently bound flavin. The covalent flavin is at the FAD level as judged by electrospray mass spectrometry. The data provide the first evidence that MTOX is a flavoprotein. The following observations indicate that 8alpha-(S-cysteinyl)FAD is the covalent flavin in MSOX from Bacillus sp. B-0618 and MTOX. FMN-containing peptides, prepared by digestion of MSOX or MTOX with trypsin, chymotrypsin, and phosphodiesterase, exhibited absorption and fluorescence properties characteristic of an 8alpha-(S-cysteinyl)flavin and could be bound to apo-flavodoxin. The thioether link in the FMN-containing peptides was converted to the sulfone by performic acid oxidation, as judged by characteristic absorbance changes and an increase in flavin fluorescence. The sulfone underwent a predicted reductive cleavage reaction upon treatment with dithionite, releasing unmodified FMN. Cys315 was identified as the covalent FAD attachment site in MSOX from B. sp. B-0618, as judged by the sequence obtained for a flavin-containing tryptic peptide (GAVCMYT). Cys315 aligns with a conserved cysteine in MSOX from other bacteria, MTOX (Cys308) and pipecolate oxidase, a homologous mammalian enzyme known to contain covalently bound flavin. There is only one conserved cysteine found among these enzymes, suggesting that Cys308 is the covalent flavin attachment site in MTOX.     

Dipolar assisted rotational resonance NMR of tryptophan and tyrosine in rhodopsin

Two dimensional (2D) solid-state (13)C.(13)C dipolar recoupling experiments are performed on a series of model compounds and on the visual pigment rhodopsin to establish the most effective method for long range distance measurements in reconstituted membrane proteins. The effects of uniform labeling, inhomogeneous B(1) fields, relaxation and dipolar truncation on cross peak intensity are investigated through NMR measurements of simple amino acid and peptide model compounds. We first show that dipolar assisted rotational resonance (DARR) is more effective than RFDR in recoupling long-range dipolar interactions in these model systems. We then use DARR to establish (13)C-(13)C correlations in rhodopsin. In rhodopsin containing 4'-(13)C-Tyr and 8,19-(13)C retinal, we observe two distinct tyrosine-to-retinal correlations in the DARR spectrum. The most intense cross peak arises from a correlation between Tyr268 and the retinal 19-(13)CH(3), which are 4.8 A apart in the rhodopsin crystal structure. A second cross peak arises from a correlation between Tyr191 and the retinal 19-(13)CH(3), which are 5.5 A apart in the crystal structure. These data demonstrate that long range (13)C em leader (13)C correlations can be obtained in non-crystalline integral membrane proteins reconstituted into lipid membranes containing less than 150 nmoles of protein. In rhodopsin containing 2-(13)C Gly121 and U-(13)C Trp265, we do not observe a Trp-Gly cross peak in the DARR spectrum despite their close proximity (3.6 A) in the crystal structure. Based on model compounds, the absence of a (13)C em leader (13)C cross peak is due to loss of intensity in the diagonal Trp resonances rather than to dipolar truncation.     

Analysis of human chorionic gonadotropin-monoclonal antibody interaction in BIAcore

Kinetic studies of macromolecular ligand-ligate interaction have generated ample interest since the advent of plasmon resonance based instruments like BIAcore. Most of the studies reported in literature assume a simple 1 : 1 Langmuir binding and complete reversibility of the system. However we observed that in a high affinity antigen-antibody system [human chorionic gonadotropin-monoclonal antibody (hCG-mAb)] dissociation is insignificant and the sensogram data cannot be used to measure the equilibrium and kinetic parameters. At low concentrations of mAb the complete sensogram could be fitted to a single exponential. Interestingly we found that at higher mAb concentrations, the binding data did not conform to a simple bimolecular model. Instead, the data fitted a two-step model, which may be because of surface heterogeneity of affinity sites. In this paper, we report on the global fit of the sensograms. We have developed a method by which a single two-minute sensogram can be used in high affinity systems to measure the association rate constant of the reaction and the functional capacity of the ligand (hCG) immobilized on the chip. We provide a rational explanation for the discrepancies generally observed in most of the BIAcore sensograms     

Pyrrolo[2,1-c][1,4]benzodiazepine-anthraquinone conjugates. Synthesis, DNA binding and cytotoxicity

New pyrrolobenzodiazepine-anthraquinone hybrids have been designed and synthesized, found to effectively bind to DNA and also exhibit cytotoxicity against many cancer cell lines     

External control in Markovian genetic regulatory networks: the imperfect information case

Probabilistic Boolean Networks, which form a subclass of Markovian Genetic Regulatory Networks, have been recently introduced as a rule-based paradigm for modeling gene regulatory networks. In an earlier paper, we introduced external control into Markovian Genetic Regulatory networks. More precisely, given a Markovian genetic regulatory network whose state transition probabilities depend on an external (control) variable, a Dynamic Programming-based procedure was developed by which one could choose the sequence of control actions that minimized a given performance index over a finite number of steps. The control algorithm of that paper, however, could be implemented only when one had perfect knowledge of the states of the Markov Chain. This paper presents a control strategy that can be implemented in the imperfect information case, and makes use of the available measurements which are assumed to be probabilistically related to the states of the underlying Markov Chain.