ABSTRACT
A novel immunoassay system based on the changes in the reflection of light, termed an optical immunoassay (OIA), was utilized to directly detect group A streptococcal (GAS) carbohydrate antigen from clinical specimens. In two studies, a total of 1,275 throat swabs were tested for the presence of this antigen with the Strep A OIA rapid detection system and the results were compared with those of standard culture methods. In both studies, the Strep A OIA yielded more positive results than plating of the throat swab onto a selective agar, Trypticase soy agar containing sheep blood, or an enriched broth. In one study, the sensitivity and specificity of Strep A OIA compared with those of the broth-enriched culture were 97.4 and 95.6%, respectively. In a second study a sensitivity of 98.9% and a specificity of 98.6% were achieved. It was also shown that the carbohydrate antigen could be detected in the absence of viable GAS organisms. The Strep A OIA is an easily interpretable method and was shown to be more sensitive than routine culture methods for detecting GAS infections directly from throat swabs.
Subject(s)
Immunoassay/methods , Pharynx/microbiology , Streptococcus pyogenes/isolation & purification , Antigens, Bacterial/analysis , Bacteriological Techniques , Culture Media , Humans , Pharyngitis/diagnosis , Pharyngitis/microbiology , Streptococcal Infections/diagnosis , Streptococcal Infections/microbiology , Streptococcus pyogenes/immunologyABSTRACT
Mouse liver asparagine aminotransferase has been found to be a mixture of enzyme forms having a cytosolic component and a mitochondrial component. The molecular weight of the mitochondrial enzyme is 70,800. The mitochondrial asparagine aminotransferase is strongly inhibited by aminooxyacetate. It is less affected by D-cycloserine but a small amount of inhibition is observed. Cysteine strongly inhibits the enzyme as do several sulfhydryl modifying reagents. The activities of the cytosolic and mitochondrial aminotransferases have been separated, and the kinetic properties of the mitochondrial form determined. The mouse liver mitochondrial asparagine aminotransferase is fairly specific for asparagine, utilizing very few amino acids as alternate amino donors and none to a great extent. The keto acid specificity is very broad, but glyoxylate is one of the most active amino group acceptors. The kinetic properties of the mitochondrial enzyme are also reported here and the data indicate strong substrate and product inhibition. Abortive complex formation may account for the deviation of the double reciprocal plots from the expected pattern.
Subject(s)
Mitochondria, Liver/enzymology , Transaminases/metabolism , Amino Acids/metabolism , Animals , Buffers , Glyoxylates/antagonists & inhibitors , Glyoxylates/isolation & purification , Glyoxylates/metabolism , Keto Acids/metabolism , Kinetics , Mice , Serine/antagonists & inhibitors , Serine/isolation & purification , Serine/metabolism , Substrate Specificity , Transaminases/antagonists & inhibitors , Transaminases/isolation & purificationABSTRACT
Asparagine aminotransferase activity was measured in a variety of mouse tissues. The liver had the highest activity--nearly 20 times more than any of the other tissues tested. Hepatic asparagine aminotransferase was found to consist of cytosolic and mitochondrial forms. The mitochondrial form was found to be the predominant form in mouse tissue. Gel filtration chromatography indicated that the mouse enzyme forms have comparable molecular weights of approximately 70,000. While the substrate specificities of the two forms are very different, asparagine was the preferred amino donor for both forms. The relative contribution to the total activity of the hepatic enzyme forms varies with the animal source. Mouse had the highest level of enzyme activity of all animals tested. Ratios of the two enzyme forms also varied greatly not only with the animal source but also with the substrate used and the isolation conditions.
Subject(s)
Cytosol/enzymology , Liver/enzymology , Mitochondria, Liver/enzymology , Transaminases/isolation & purification , Amino Acids/pharmacology , Animals , Cattle , Columbidae , Glyoxylates/antagonists & inhibitors , Glyoxylates/isolation & purification , Glyoxylates/metabolism , Guinea Pigs , Keto Acids/metabolism , Mice , Rats , Serine/antagonists & inhibitors , Serine/isolation & purification , Species Specificity , Substrate Specificity , Transaminases/antagonists & inhibitorsABSTRACT
Methotrexate was found to stimulate asparagine synthetase activity in vivo by approximately six-fold in rat liver. The maximum effect of methotrexate on hepatic asparagine synthetase activity was observed sixteen hours after intraperitoneal injection of the drug. Cycloheximide, like methotrexate, is a protein synthesis inhibitor and was used to determine that asparagine synthetase activity was not preferentially stimulated under stress. As expected, hepatic asparagine synthetase activity falls markedly with the decreased protein synthesis caused by injection of cycloheximide. It is proposed that methotrexate inhibits serine-dependent glycine biosyn-thesis by decreasing the concentration of tetrahydrofolate for serine hydroxymethyltransferase. This leads to a stimulation of asparagine synthetase to provide nitrogen for asparagine-dependent glycine synthesis. This may provide an explanation of the observed chemotherapeutic synergism between asparaginase and methotrexate treatment.
