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Biomedical subjects

R F Chen

Publications and source records attributed to R F Chen.

At least 73 records · Page 4Linked to original sources
PubMed1970

Lactate dehydrogenase isozymes: further kinetic studies at high enzyme concentration.

By competition with lactate dehydrogenase (LDH) for nicotinamide adenine dinucleotide (NAD), commonly occurring intracellular proteins, such as glyceraldehyde-3-phosphate dehydrogenase, malate dehydrogenase, and albumin, can protect LDH-1 and LDH-5 from inhibition and ternary complex formation with NAD and pyruvate. The existence of intracellular proteins that compete with LDH for NAD renders unphysiological a model for estimating the extent of intracellular LDH inhibition based on incubations of only LDH, NAD, and pyruvate.

Glyceraldehyde-3-Phosphate Dehydrogenases↗
PubMed1970

Kinetics of folding of staphylococcal nuclease.

Staplhylococcal nuclease undergoes a reversible structural transition between (p)h3 and 4 which be mesured by changes in tryptoham fluorescence. A stopped-flow spectrofluorometer was used to study the kinetics renaturation of nuclease from the acidified form on neutralization, the refolding is fast and the data can be described as a sequence of two first-order processes with half times of about 55 and 350 milliseconds, respectively.

Enzymes↗
PubMed1970

Lactate dehydrogenase isozymes: kinetic properties at high enzyme concentrations.

The kinetic properties of lactate dehydrogenase (LDH) isozymes have been determined at high enzyme concentrations. Spectrophotofluorometric assays revealed that the extent of substrate inhibition of LDH-1 and LDH-5 depends on enzyme concentration. At high enzyme concentrations, in the range of those that exist in most mammalian cells, no inhibition by pyruvate occurred. Pyruvate concentrations up to and including 20.0 millimoles per liter were used for each isozyme at 25 degrees and 40 degrees C at pH 7.0 and 7.4. These results suggest that substrate inhibition of LDH may not occur in vivo but only in vitro after appreciable dilution from physiologic enzyme concentrations. These experiments provide further evidence against the theory that substrate inhibition of LDH-1 in vivo accounts for the distribution of LDH isozymes within various tissues. They raise the possibility that, for other enzymes, kinetic properties determined at highly dilute concentrations in vitro may also be quite different from kinetic properties at the much higher concentrations that exist in vivo.

Animals↗
PubMed1967

Fluorescence decay times: proteins, coenzymes, and other compounds in water.

The fluorescence decay time (tau) was 2 to 5 nanoseconds for proteins and 4 to 5 nanoseconds for flavin, pyridine nucleotide, and vitamin B(6)coenzymes; tau varied widely in 48 compounds measured in water. Altholugh reported values of tau for a few of the soluttions studied were in excellenlt agreement. previously "calculated" lifetimes, in severall instances, are apparently erroneous. Nonexponential decay was detectable with our "nanosecond-flash" apparatus, a modification of the first commercially aavilable unit for determination of tau.

Chemical Phenomena↗