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PubMedDate not supplied

[Kinetic characteristics of DNA alkylation with some chloroethylmethylarylamines and elimination of alkylated bases from DNA].

Kinetics of DNA alkylation with 2',3'-o-[N-2-chloroethyl-N-methylamino)benzylidene]uridine (UCHRCL), uridine-5'-methylphosphate (MepUCHRCL) and 4-(N-2-chloroethyl-N-methylamino)benzylamine (NH2CH2RCl) and kinetics of elimination of alkylated bases have been studied. Efficiency of DNA alkylation (p/s-ratio of rate constant of alkylation to the sum of rate constants of by-reactions of an active intermediate formed from the reagent) increases with an increase of the positive charge of the reagents as well as efficiency of tRNA alkylation. Alkylated bases are eliminated from DNA; rate of elimination depends on the structure of the reagent; it decreases in the series NH2CH2R- greater than greater than UCHR-greater than MepUCHR-. Bases alkylated by NH2CH2RCl and UCHRCl are eliminated from DNA during alkylation; therefore plots of DNA alkylation by NH2CH2RCl have a maximum. DNA alkylated by MepUCHRCl is rather stable; alkylated bases are not eliminated during alkylation. Effect of temperature and pH on elimination has been studied.

Alkylating Agents↗
PubMedDate not supplied

[Isolation and properties of polyphosphatase of Neurospora crassa].

Polyphosphatase (polyphosphate-phosphohydrolase) has been isolated from mycelium of Neurospora crassa and purified to homogenous state. The enzyme is shown to be strictly specific to high molecular weight inorganic polyphosphates. Km for phosphate in polymeric form is 6.8-10(-4) M. The molecular weight of this enzyme is 50 000 +/- 3000. To display its activity polyphosphatase requires the presence of bivalent cations of some metals, Mg2+ ions being the best activator with Co2+, Mn2+ and Fe2+ ions-slightly less effective.

Cations, Divalent↗
PubMedDate not supplied

[Isolation of rat liver chromatin non-histone protein].

A chromatin with the protein/DNA ratio of 3.0 was obtained from rat liver cells nuclei. The chromatin was dissolved in 2 M NaCl, pH 7, and reprecipitated by decreasing the ionic strength to 0.4 and increasing pH to 9.0. A fraction of non-histone proteins (NH-1) remained in a supernatant solution, the NH-1/DNA ratio being equal to 1.3 and the ratio of acidic to basic aminoacid residues equal to 1.31. After chromatography on Bio-Rex 70 cation-exchang resin, a fraction (NH-2) with the NH-2/DNA ratio of 1.0 +/- 0.15 and the ratio of acidic to basic aminoacid residues of 1.57 was obtained. According to the data of polyacrylamide gel electrophoresis, the NH-2 fraction contained 2.7% of histone f2 + f3 as an admixture whereas histone f1 was not revealed.

Amino Acids↗
PubMedDate not supplied

[pH-dependence of the mechanism of pepsin action].

N-Acetyl-L-phenylalanine inhibition of the peptic hydrolysis of N-acetyl-L-phenylalanine-L-tyrosine over the pH range 2-4.5 was studied. The mixed character of inhibition which was partially competitive and partially non-competitive allowed us to infer that the separate steps of the enzymatic hydrolysis were pH dependent. The orderliness of the dissociation of the triple enzyme-product-product complex was also pH dependent. The group with pKa approximately 3 influenced the mechanisms of pepsin hydrolysis as strongly as in the case of pepsin catalyzed oxygen isotopic exchange in the acyl amino acid carboxyl group.

Binding Sites↗
PubMed1975

Effect of variations in pH on kinetics of myosin.

The pH optimum was the same in canine tissue for cardiac and skeletal muscle myosin; when myosin was activated by monovalent cations, the pH optimum was 7.5 while activation of myosin by divalent cations gave a pH optimum of 5.5. Protons were needed for divalent cation activation of myosin. With changes in pH there were concomitant changes in the apparent affinity of enzyme for substrate (S 0.5), such that with a decrease in pH there was an elevation in K+- or NH4+ -activated myosin's apparent affinity for adenosine triphosphate (ATP), and at the same time a decrease in Vmax values of myosin. The converse was true with the divalent cations, Ca++ and Mn++; here with a decrease in pH there was a concomitant decrease in apparent affinity of myosin for ATP, and at the same time an increase in the enzymatic Vmax values. It appeared that hydrogen ions affected the apparent affinity of myosin for substrate and this in turn affected the rate-limiting step in ATPase reaction. Addition of monovalent cations to the divalent cation activating system lowered the activity of myosin, and the converse was true: divalent cations lowered the activity of myosin when activated by monovalent ones in a monovalent cation activating system.

Adenosine Triphosphatases↗
PubMed1975

Normal blood-gas values in lambs during neonatal development and in adult sheep.

Arterial oxygen (PaO2) and carbon dioxide (PaCO2) tensions and pH were determined in 20 lambs during development from two weeks to five months of age and in 34 adult sheep. Throughout the period the lambs' mean PaCO2 (33.1 mm Hg) and pH (7.46) values were similar to those determined in the adult sheep (PaCO232.1 mm Hg; pH 7.48). The lamb's mean PaO2 increased from 63.3 mm Hg at two weeks of age to about 80 mm Hg at eight weeks and by 20 weeks was similar to the mean PaO2 (88.0 mm Hg) of adult sheep.

Animals↗
PubMed1975

Identification of dimethylnitrosoamine metabolites in vitro.

The incubation of dimethylnitrosoamine (DMNA) in the presence of rat liver microsomes leads to production of formaldehyde, formic acid, methylamine, and N-methylhydrazine. When pH 5-enzymes are added to the medium there is also the formation of N-methylhydroxylamide and N,N-dimethylhydrazine. The last compound is the only metabolite produced, to a lesser extent, by the pH 5-enzymes. Thus, the denitrosated or non-denitrosated metabolites are produced either by an oxidative dealkylation and by a reduction of DMNA, catalysed by microsomal and cellular soluble enzymes.

Animals↗
PubMed1975

Degradation of dimethylnitrosoamine catalysed by physical and chemical agents.

Decomposition of dimethylnitrosoamine (DMNA) by chemical and physical agents was further investigated. Both photoirradiation with sunlight or ultraviolet ray and reductive reactions under acid conditions (likely occurring in the stomach) led to the formation of formaldehyde, formic acid, and N-methydrazine, in addition to denitrosated compounds such as methylamine, dimethylamine, and N-methylhydroxylamine. N-Methylhydrazine was the only compound which was not detected by photoirradiation under neutral conditions. The agreement between physiochemical and metabolic degradation products and the possible biological meaning are discussed together with the problem of environmental contamination by the nitroso compound.

Dimethylnitrosamine↗
PubMed1976

Hydrogen exchange at the amide group of reduced pyridine nucleotides and the inhibition of that reaction by dehydrogenases.

Stopped flow ultraviolet spectroscopy has been used to measure the rate of hydrogen exchange with solvent at the amide group of reduced nicotinamide nucleotide coenzymes. Several mechanisms for the exchange reaction are considered in the light of the kinetic data. Complex formation between the coenzyme and any of four dehydrogenases markedly slows the rate of hydrogen exchange. Hydrogen bond formation and/or hydrophobic interactions within these complexes are thought to be the reasons for the decreased rate of exchange.

Alcohol Oxidoreductases↗
PubMedDate not supplied

[Metabolic acidosis and intravenous injections of fat emulsions (role of phospholipids. Experimental study)].

In explanation of metabolic acidosis during parenteral nutrition, the authors considered the supply of H+ ions by fat emulsion, containing phospholipids of egg or soy. During intravenous infusions of 24 grams of lecithins to two healthy subjects, they observed an increased output H+ ions in urine, about 74,05 and 75,88 mEq, and a metabolic acidosis of the plasma. The theorically forcasted supply of production was 74,6 mEq. Indeed the metabolism of phospholipids supplies phosphoric ions (PO4H3), giving H+ ions at pH 7,40. The most used fat emulsions are able to give between 37 (intralipid 10%) and 61 (lipihysan 15%) mEq of H+ ions/liter.

Acidosis↗
PubMed1975

[Endocrine cells of the gastric mucous membrane].

In order to obtain an additional information concerning a possible functional role of the main types of the endocrine cells (EC and ECL) on investigation of aspiration biopsy specimens taken from the middle third of the stomach in patients with ulcerative disease of the duodenum and chronic gastritis was carried out. Changes in morphology, distribution and number of the endocrine cells in pathology of the mucosa and in various acidity of the gastric juice were followed up. On the basis of the data obtained the conclusion is made that serotonin-producing (EC) cells seem to have nothing to do with the regulation of the activity of the fundal glands, whereas the enterochromaffin-like cells (ECL) influence the production of hydrochloric acid by pavement cells.

Chronic Disease↗
PubMed1976

[Old and new dangers of blood transfusion (author's transl)].

The predominant danger of blood transfusion, even after the discovery of the ABO and Rh systems, is the immunological risk. This led in 1940 to a regulation of blood transfusion in Germany by official guidelines which were constantly adjusted in the light of new research results. The dangers due to deterioration on storage still receive too little attention although these may be of greater danger to the patient than immunisation risk. Also the assessment of other medical problems of transfusion is insufficiently applied to clinical routine.

Ammonia↗
PubMed1977

Biosynthesis of alpha-amylase and protease by Streptomyces olivaceus 142. I. Regulation of alpha-amylase activity.

Streptomyces olivaceus 142 produces amylase in the logarithmic phase of growth of the culture. The synthesis of the enzyme is induced by maltose and starch. In the case of maltose the synthesis is induced by a contaminating compound, probably being a higher than maltose polymer of glucose. The synthesis of amylase is negatively controlled by catabolic repression. The level of the activity of the enzyme depends not only on the biosynthesis but also on it proteolytic degradation.

Amylases↗