2-Aminoethylarsonic acid was tested for its ability to act as a substrate for ethanolamine-phosphate cytidylytransferase as a cytidylyl acceptor in place of ethanolamine phosphate. The expected product, like all mixed anhydrides of arsonic acids, should hydrolyse spontaneously with regeneration of the substrate analogue and CMP formation; such CMP production was observed. The limiting velocity ...

Measuring the initial velocity is difficult in some enzyme assays where a significant fraction of the substrate is consumed. Here a solution to this problem is proposed; the time to produce a fixed amount of reaction product is measured. This time is inversely proportional to the initial velocity, and is related to the maximum velocity and Michaelis constant by a simple equation and linear plot...

The effect of protein binding on kidney function has been studied by investigating the renal accumulation and secretion of the hippurate analogue 2-methylbenzoylglycine in the isolated perfused rat kidney in the absence and presence of bovine serum albumin (BSA). Experiments were performed with either 2.5% pluronic or a combination of 2.2% pluronic and 2% BSA as oncotic agents; a wide concentra...

a simple mathematical model of steady state  oxygen distribution subject to diffusive transport and non- linear uptake in a retinal cylinder has been developed. the approximate analytical solution to a reaction- diffusion equation are obtained by using series expansions. the computational results for the scaled variables are presented through graphs. the effect of the important parameters (1) d...

The steady state kinetics of calcium transport driven by ATP hydrolysis and ATP synthesis catalyzed by purified, reconstituted calcium ATPase has been investigated as a function of the transmembrane calcium gradient. Purified calcium ATPase was reconstituted into phospholipid vesicles enabling control of the transmembrane calcium gradient. Calcium transport was monitored spectrophotometrically ...

At low extracellular pH (4-6), net uptake of potassium by Neurospora is a simple exponential process which obeys Michaelis kinetics as a function of [K](o). At high pH, however, potassium uptake becomes considerably more complex, and can be resolved into two distinct exponential components. The fast component (time constant = 1.2 min) is matched quantitatively by a rapid loss of sodium; it is a...

Preliminary evidence has suggested that hexokinase in rat heart changes its kinetic properties in response to insulin through translocation to the outer mitochondrial membrane. We reexamined this hypothesis in light of tracer kinetic evidence to the contrary. Our methods were as follows. Working rat hearts were perfused with Krebs-Henseleit buffer containing glucose (5 mmol/l) and sodium oleate...

1. The interconversion of hydroxypyruvate and l-glycerate in the presence of NAD and rat-liver l-lactate dehydrogenase has been demonstrated. Michaelis constants for these substrates together with an equilibrium constant have been determined and compared with those for pyruvate and l-lactate. 2. The presence of d-glycerate dehydrogenase in rat liver has been confirmed and the enzyme has been pu...

OBJECTIVES The aim of this article is biochemical and kinetic characterization of CTX-M-43, a natural Asp-240-->Gly mutant of CTX-M-44 (ex Toho-1), from a clinical isolate of Acinetobacter baumannii isolated in a Bolivian hospital. METHODS Steady-state kinetic parameters (K(m) and k(cat)) were determined for a large pattern of substrates. Analysis of inactivators and transient inactivators wa...

Influx and efflux of choline in human erythrocytes were studied using (14)C-choline. When incubated at 37 degrees C with physiological concentrations of choline erythrocytes concentrate choline; the steady-state ratio is 2.08 +/- 0.23 when the external choline is 2.5 microM and falls to 0.94 +/- 0.13 as the external concentration is raised to 50 microM. During the steady state the influx of cho...