PubMed Health⌕ Search

Biomedical subjects

A C Frasch

Publications and source records attributed to A C Frasch.

105 records · Page 6Linked to original sources
PubMed1980

The genes for variant antigens in trypanosomes.

We have studied the mechanism of antigenic variation by using DNA complementary to the messenger RNAs for four variant surface glycoproteins of Trypanosoma brucei. Pure complementary DNAs were obtained by cloning as recombinant DNA in Escherichia coli. Using these complementary DNAs as hybridization probes, we have analyzed the genes for these variant surface glycoproteins. The results provide new information on the origin and evolution of antigenic variation, and on the mechanism involved in switching from one antigenic type to another.

Animals↗
PubMed1979

Two forms of 'malic' enzyme with different regulatory properties in Trypanosoma cruzi.

1. Cell-free extracts from culture epimastigotes of Trypanosoma cruzi contained two forms of NADP+-linked 'malic' enzyme (EC 1.1.1.40), I and II, with the same molecular weight but different electrophoretic mobilities and kinetic and regulatory properties. 2. The apparent Km for L-malate was lower for 'malic' enzyme I, with hyperbolic kinetics, whereas the kinetic pattern for 'malic' enzyme II was slightly sigmoidal (h 1.4). The kinetics for NADPH were hyperbolic for 'malic' enzyme I, and very complex for 'malic' enzyme II, suggesting both positive and negative co-operativity. 3. 'Malic' enzyme II was markedly inhibited by adenine nucleotides; AMP was the the most effective, at least in the presence of an excess of MnCl2. 'Malic' enzyme I was much less affected by the nucleotides. Both enzyme forms were inhibited by oxaloacetate, competitively towards L-malate, but the apparent Ki for 'malic' enzyme I (9 microM) was 10-fold lower than the value for 'malic' enzyme II. 'Malic' enzyme II, but not 'malic' enzyme I, was activated by L-aspartate and succinate (apparent Ka of 0.12 and 0.5 mM respectively); the activators caused a decrease in the apparent Km for L-malate and, to a lesser extent, in the apparent Km for NADP+. L-Aspartate, but not succinate, increased the apparent Vmax. 4. The inhibition by AMP suggests regulation by energy charge, with the L-malate-decarboxylation reaction catalysed by 'malic' enzyme II fulfilling a biosynthetic role. The inhibition by oxaloacetate and the activation by succinate are probably involved in the regulation of the 'partial aerobic fermentation' of glucose which yields succinate as final product. The activation by L-aspartate would facilitate the catabolism of this amino acid, when present in excess in the growth medium.

Adenine Nucleotides↗
PubMed1978

Adenosine triphosphatase activities in Trypanosoma cruzi.

1. Subcellular fractions obtained from epimastigotes of Trypanosoma cruzi, disrupted by three different procedures, contained in addition to the already known Mg2+-activated adenosine triphosphatase (ATPase; E.C.3.6.1.4), a Ca2+-ATPase activity. 2. The Ca2+-ATPase (a) was activated by low concentrations of CaCl2 (apparent Ka, 80 microM); (b) had a Km for ATP of 0.6 mM (at 1 mM CaCl2, pH 8.0); (c) presented a broad pH curve (optimum 7.1-8.6); and (d) was insensitive to oligomycin concentrations which inhibited the Mg2+-ATPase present in the same preparations. 3. All attempts to find a (Na+-K+)-activated, ouabain-inhibited, ATPase have been unsuccessful, in spite of the fact that living epimastigoes of T. cruzi are able to concentrate K+ and exclude Na+ from the medium.

Adenosine Triphosphatases↗
PubMed1978

Solubilization and some properties of the Mg2+-activated adenosine triphosphatase from Trypanosoma cruzi.

1. Grinding of epimastigotes of Trypanosoma cruzi with glass powder in a mortar yielded a Mg2+-activated adenosine triphosphatase (ATPase) preparation which was highly sensitive to oligomycin. 2. Chloroform treatment of the particles resulted in the solubilization of an ATPase which was (a) activated by MgCl2; (b) slightly inhibited by CaCl2; (c) activated by sulphite and bisulphite; (d) had an optimum pH of 7.6; and (e) had a Km for ATP of 2.1 mM (in the presence of 4 mM MgCl2). 3. The solubilized enzyme was insensitive to oligomycin and leucinostatin, which inhibited the membrane-bound ATPase, though inhibited by efrapeptin and quercetin. 4. The results indicate that the chloroform-extracted enzyme is a soluble F1-ATPase similar to those isolated from mammalian mitochondria.

Animals↗
PubMed1978

Microspectrophotometric quantitation of the diaminobenzidine reaction for histochemical demonstration of cytochrome oxidase activity.

Polyacrylamide models in which an extract of cattle heart mitochondria was incorporated, as well as cryostat sections of tongue muscle and epithelium, were used to set up the conditions under which the histochemical reaction for the demonstration of cytochrome oxidase can be quantitated. Using diaminobenzidine in a concentration of 5.5 mM, cytochrome C in a fixed concentration of 76 micron and keeping the incubation medium away from direct light action, enzyme activity can be evaluated by means of direct microphotometry on tissue sections. Each biologic model requires previous individual determination of the measurement limits. These limits can be readily established by using a small chamber for the incubation medium, which can be placed in the microphotometer, allowing the reaction rate to be following using a single section.

3,3'-Diaminobenzidine↗
PubMed1976

Sulphydryl and disulphide groups in normal and irradiated epidermis.

The distribution of sulphydryl (SH) and disulphide (SS) groups in normal and irradiated epidermis of newly-born rats was studied by microspectrophotometric quantitation of the Mercury-Orange reaction. In order to obtain information on (1) the total content of both groups within the different strata of the epithelium, and (2) the mean SH and SS concentration, which is an indicator of the density of these groups per unit of tissue. The content of both groups increased in relation to the extent of irradiated area, whereas there was a decrease in the mean concentration. The increase in content of SH and SS would lead to augmented production of keratin substance previously reported in irradiated epithelia, coincidentally with an acanthotic response. The decrease in concentration of SH and SS indicates a destruction of these groups at cellular level, which may be due to membrane alterations. The findings would explain an acceleration of the keratinizing process together with modifications, both in quality and in quantity, in the horny substance.

Animals↗
PubMed1976

Ultrastructural localization of acid phosphatase in normal and X-irradiated epidermis.

Acid phosphatase activity has been studied in normal and X-irradiated rat epidermis. A remarkable reaction increment was found in irradiated epithelium at the granular layer keeping the same pattern of distribution observed in the normal tissue. No reactive lysosomes or keratinosomes were observed in the cytochemical sections, while many keratinosomes but no lysosomes appeared in the electron microscopic preparations of irradiated animals. Irradiated epithelium is discussed as a suitable model to analyze the role of acid phosphatase in the keratinization mechanisms.

Acid Phosphatase↗
PubMed1975

A quantitative microspectrophotometric study of the lead precipitation reaction for the histochemical demonstration of acid phosphatase.

The possibility of quantitating microspectrophotometrically the lead precipitation reaction for the histochemical demonstration of acid phosphatase was studied using the following models: sections of rat kidney and human prostate gland, and polyacrylamide films with incorporated prostate gland homogenate. The activity of the polyacrylamide models was previously evaluated by a biochemical method and the specificity of the reaction was controlled with specific inhibitors. Linear relations between cytophotometric reading and enzymatic activity, and between optical densities and different incubation periods, were demonstrated. The results obtained indicate the validity of the microspectrophotometric quantitation for this reaction with direct readings over a wide range of the visible light spectrum.

Acid Phosphatase↗
PubMedDate not supplied

Chromosomal localization of seven cloned antigen genes provides evidence of diploidy and further demonstration of karyotype variability in Trypanosoma cruzi.

The karyotype of Trypanosoma cruzi was studied by pulsed field gel electrophoresis (PFGE) in conditions that allowed 20-25 chromosome bands to be detected. However, several of these bands were present in non-equimolar amounts, suggesting that the total chromosome number is considerably higher. The patterns obtained with the different cloned and uncloned strains were unique, suggesting that the karyotype of T. cruzi is highly variable. The chromosomal localizations of seven cloned genes were determined by Southern blotting of PFGE-separated chromosomes. Three of the clones gave rise to similar patterns and mapped on a chromosome or a family of chromosomes larger than 1.6 Mb. Two clones mapped on either single or pairs of chromosomes, which in some cases differed considerably in size between the different strains tested, suggesting that extensive chromosome rearrangements occur in T. cruzi. Another clone hybridized to several chromosomes in most strains and probably represents a family of genes. Lastly, one clone hybridized to nearly all chromosomes. Many of the clones hybridized to pairs of restriction fragments in the different strains, suggesting that they are allelic. For one of the clones it was possible to provide further evidence for the allelic nature of the fragments by establishing detailed restriction maps around them and by showing that the two fragments in a pair hybridized to chromosomes which differed slightly in size. Taken together, the results infer that the genome of T. cruzi epimastigotes is diploid.

Animals↗