PubMed Health⌕ Search

Biomedical subjects

C Brownson

Publications and source records attributed to C Brownson.

30 records · Page 2Linked to original sources
PubMed1973

The modification of cholinesterase activity by 5,5'-dithiobis-(2-nitrobenzoic acid) included in the coupled spectrophotometric assay. Evidence for a non-catalytic substrate-binding site.

1. Compared with the acetylcholinesterase assay carried out in the absence of a dithiol, the presence of 5,5'-dithiobis-(2-nitrobenzoic acid) caused marked activation, 6,6'-dithiodinicotinic acid and 2,2'-dithiobis-(5-nitropyridine) less so and 2,2'-dithiodipyridine (aldrithiol-2) had no effect at all. Measurements are further complicated in that the 5-thio-2-nitrobenzoate ion also appears to interact with the enzyme, resulting in slightly lowered absorbance values. 2. Acetylthiocholine competes for the 5,5'-dithiobis-(2-nitrobenzoic acid)-binding site so that activation is essentially eliminated by saturating concentrations of substrate. The presence of the dithiol decreases the K(m) value of acetylthiocholine. 3. Similar results were obtained with pseudocholinesterase. However, with butyrylthiocholine clear activation was still observed under V(max.) conditions in addition to K(m) being lowered. 4. All the data yielded Hill coefficients of 1 and analysis of the results leads to the conclusion that activation results from the dithiol being bound to a site on the subunit that is actively catalysing ester hydrolysis. 5. The use of aldrithiol-2 is recommended for kinetic work where absolute quantitative measurements are required.

Benzoates↗
PubMed1972

Partial purification and properties of the two common inherited forms of human erythrocyte adenylate kinase.

1. The partial purification of adenylate kinase, types 1 and 2, from human erythrocytes is described. 2. Gel chromatography of both forms of the enzyme gave estimates of the molecular weights in the range 20000-23000. 3. Studies on crude haemolysates at various pH values indicated that the type 2 enzyme was less stable than the type 1. Heat denaturation studies on the partially purified enzymes confirmed these findings. 4. Measurements of rates of inhibition by iodoacetate and iodoacetamide showed that the type 2 enzyme reacts more readily than the type 1 enzyme with both reagents. 5. The effect of temperature on the initial velocity of ADP formation was measured at a single concentration of both AMP and MgATP(2-). The two forms of the enzyme responded differently to increasing temperature.

Adenosine Diphosphate↗
PubMed1972

Kinetic studies on the two common inherited forms of human erythrocyte adenylate kinase.

1. The kinetic properties of two genetic variants of human erythrocyte adenylate kinase were studied at limiting concentrations of both ADP and MgADP(-) in the forward direction and at limiting concentrations of both AMP and MgATP(2-) in the reverse direction. 2. Primary reciprocal plots rule out the possibility of a Ping Pong mechanism for both forms of the enzyme. 3. Analysis of the kinetic data by an appropriate computer program gave the following K(m) values for the type 1 enzyme: AMP, 0.33mm+/-0.1; MgATP(2-), 0.95mm+/-0.13; ADP, 0.12mm+/-0.03; MgADP(-), 0.22mm+/-0.04. Values for the type 2 enzyme were: AMP, 0.27mm+/-0.03; MgATP(2-), 0.40mm+/-0.05; ADP, 0.08mm+/-0.07; MgADP(-), 0.20mm+/-0.04. 4. Product inhibition studies were done by studying the reverse reaction. With ADP as product inhibitor competitive inhibition patterns were obtained with AMP and/or MgATP(2-) as variable substrate. Similar results were obtained for product inhibition by MgADP(-) with AMP as variable substrate. The results are consistent with a Rapid Equilibrium Random mechanism. 5. Secondary plots of slope versus product concentration were linear. The data were fitted to the appropriate equation and analysed by computer to give values for the product inhibition constants. 6. Differences between the values of certain kinetic constants for the two forms of the enzyme were observed.

Adenosine Diphosphate↗
PubMedDate not supplied

Electrical stimulation modulates IGF binding protein transcript levels in C2C12 myotubes.

Electrical stimulation (ES) of skeletal muscle can produce changes in metabolic enzyme and contractile protein gene expression resulting in fast-to-slow phenotypic changes. The molecular mechanism by which ES induces changes in phenotype is not entirely understood but recent reports have demonstrated that the calcineurin/NF-AT signalling pathway is involved. IGF-1 is also capable of inducing changes in phenotype through the same calcineurin/NF-AT pathway but little is known of the direct effect of ES on the IGF system. In this study, we examined the effects of ES on the expression of igf-1, igf-2 and the six igfbp genes in the C2C12 muscle cell line. Results showed that ES induced a change in phenotype that was accompanied by downregulation of igf-2 and upregulation of igfbp-4 mRNA levels. However, ES did not significantly alter the transcription of igf-1, igfbp-2, igfbp-5 and igfbp-6 genes. This study demonstrates that ES of muscle cells in vitro not only directly modulates the gene expression of contractile proteins but also modulates proteins that are part of the IGF regulatory system, in particular IGFBP-4.

Animals↗