Biomedical subjects

J Chrastil

Publications and source records attributed to J Chrastil.

15 recordsLinked to original sources

PubMed1992

A group additivity model for analyzing absorption spectra of organic compounds: applications to partial structural analysis and molecular weight determinations of polymers, nucleotides, and peptides.

A new method for the analysis of organic structural groups from absorption spectra is described. The method is based on the integrated intensity of absorption. It requires only micrograms of analyzed compound, which may be fully recovered after analysis from its solution. The method can be used for different kinds of structural and/or kinetic studies. For example, the reaction kinetics and tautomeric equilibria can be easily studied by this method. The method can also be used for the determination of molecular weight and quantitative composition of polymers, nucleotides, and/or peptides. Hydrolysis or derivatization of the studied compounds is not necessary. On the basis of this method, automatic molecular weight, nucleotide, and peptide analyzers can be constructed.

Hydrogen-Ion Concentration↗

PubMed1990

Spectrophotometric determination of cysteine and cystine in urine.

A spectrophotometric method for the determination of cysteine and cystine in urine is described. This method is a modification of that reported for the determination of cysteine and cystine in proteins. The determination in urine is specific and simple. The colour develops at room temperature and no pre-treatment of urine is needed. Other amino acids, urea, uric acid, ascorbic acid, bilirubin, biliverdin, carbohydrates, hormones, acetone, salicylic acid, small amounts of protein and other common components of urine do not interfere. The method is particularly suitable for the diagnosis of hepatic cystinuria and other diseases characterised by high sulphur-containing amino acids in urine.

Cysteine↗

PubMed1988

Enzymic product formation curves with the normal or diffusion limited reaction mechanism and in the presence of substrate receptors.

1. The enzymic product formation curves for several enzymes have been studied. 2. The product formation kinetics was related to the initial velocity kinetics and to the diffusion rate limited kinetics. 3. The time curves revealed new constants characterizing structural and binding properties of the enzymic systems which are not revealed from initial velocities. 4. The influence of selected inhibitors on the time curves has been studied. 5. The time curves revealed the specific substrate-receptor binding which was not revealed from initial velocities. 6. The product formation kinetics of acid phosphatase, beta-amylase and NADPH2 cytochrome-c reductase in the absence and in the presence of inhibitors, mercuric acetate and o-iodosobenzoate is described. 7. The time curves revealed the binding of cytochrome-c to the specific natural protein receptors. 8. The activation energies of acid phosphatase and beta-amylase were determined from the time curves.

Acid Phosphatase↗

PubMed1986

Spectrophotometric determination of tryptophan and tyrosine in peptides and proteins based on new color reactions.

A new spectrophotometric method for quantitative determination of tryptophan and tyrosine in peptides and proteins is described. It is based on two specific color reactions, the reaction of tryptophan with formaldehyde and the reaction of tyrosine and tryptophan with hydroxylamine and ceric cations. By combination of these two reactions both tyrosine and tryptophan can be determined simultaneously. Tyrosine and/or tryptophan bound in peptides and/or proteins react independently of the rest of the peptide or protein molecule. The method is simple, accurate, and sensitive. Hydrolysis is not necessary.

Cerium↗

PubMed1979

Inhibition of drug oxidation and stimulation of NADPH oxidase in vitro by doxorubicin and triferric-doxorubicin.

The electrophilic properties of the quinone-hydroquinone configuration of anthracycline antibiotics suggests a possible influence on cytochrome P-450-mediated mono-oxygenase reactions. Both doxorubicin and triferric-doxorubicin (a derivative in which the quinone groups are blocked with iron) showed a similar dose-dependent inhibition of liver microsomal drug metabolism. A doxorubicin concentration-related stimulation of NADPH oxidase activity was found to be linear but that for triferric-doxorubicin was asymptotic. Neither inhibitor affected the activity of cytochrome c reductase, cytochrome b5 reductase or cytochrome P-450 reductase. However, doxorubicin did potentiate the inhibitory effect of aniline on cytochrome P-450 reductase and on ethylmorphine metabolism. It is concluded that these anthracyclines inhibit drug metabolism in vitro not by their electron-withdrawing potential but in a manner more similar to that described for type II compounds.

Aminophenols↗

PubMed1978

Quantitative estimation of salicylic acid and its metabolites by thin-layer densitometry.

A rapid thin-layer densitometric method for the quantitative determination of salicylic acid and its metabolites in urine or plasma is described. The method is specific and very sensitive. Nanogram quantities of salicylic acid and its metabolites, both free and conjugated, may be estimated. Known metabolites, as well as the newly described gentisuric acid, were estimated quantitatively in urine from a patient treated with aspirin.

Aspirin↗

PubMed1978

Contribution of cytochromes and proteins to the effect of ascorbic acid on artificial and microsomal hydroxylation systems containing oxygen and hydrogen peroxide.

Hydroxylation systems containing cytochromes, proteins and ascorbic acid were studied at physiological pH (7.4) under O2 or N2 with added H2O2. Proteins inhibited aromatic hydroxylation of p-nitrophenol or oxidative demethylation of ethylmorphine in ascorbic acid-containing systems incubated under O2, but strongly activated the systems containing H2O2. Cytochrome c and partially purified cytochrome P-450 from rat liver microsomal preparations activated the system in either O2 or H2O2. The systems needed ascorbic acid (or other enol structures) for activation. Cytochrome iron participated probably in the activation of O2, whereas cytochrome protein participated in a free radical activation of H2O2 (or of O2).

Animals↗

PubMed1978

Gentisuric acid: metabolic formation in animals and identification as a metabolite of aspirin in man.

Gentisuric acid was synthesized from gentisic acid and glycine ethyl ester. NMR, mass spectrometric and elemental analysis confirmed the product as GU, and physicochemical characteristics were determined. A TLC-densitometric technique was developed to estimate GU and other metabolites of aspirin. Conjugation of gentisic acid with glycine to form GU was catalyzed by a mitochondrial fraction of rat and beef liver. GU was also formed by the rat liver microsomal hydroxylation of salicyluric acid, and phenobarbital pretreatment increased this formation. A random survey showed GU in 76% of SA-positive urines from aspirin-treated patients. Identity of GU in urine from two aspirin-treated patients was confirmed by TLC and mass spectrometric analysis, and hydrolysis of the compound from one patient yielded glycine and gentisic acid. Urine from controls or post-aspirin treatment patients did not show GU by TLC analysis. These results demonstrate for the first time the metabolic formation of GU in animals and its occurrence as a metabolite of aspirin in man.

Acyltransferases↗

PubMed1976