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Biomedical subjects

D Garfinkel

Publications and source records attributed to D Garfinkel.

At least 109 records · Page 6Linked to original sources
PubMed1975

Computer simulation of the metabolism of guinea pig brain slices, and how they differ from the intact brain.

A computer model of the metabolism of glutamate, glutamine, gamma-aminobutyrate and the Krebs cycle in guinea pig cortex slices has been constructed in terms of 98 reactions among 38 unlabeled species. Fitting the data from slices required the addition of a third small compartment to previous 2-compartment models based on whole brain experiments. This third compartment corresponds to the tissue damaged during the slicing process, and dominates the metabolism of 14C-labeled substrates at early times. The times required for equilibration between this additional compartment and the bulk of the slice are no longer than expected. Interpretation of short-term slice experiments may be subject to appreciable error owing to the presence of this additional compartment.

Acetates↗
PubMed1975

Biochemistry and genetics of Klebsiella pneumoniae mutant strains unable to fix N2.

Selected mutant strains of Klebsiella pneumoniae that are unable to fix nitrogen have been characterized according to nitrogenase component activity as well as antigenic cross-reacting material. The lesions in these strains have been mapped by transduction, and the results indicate that there are at least five genes specifically responsible for nitrogen fixation in vivo. Besides genes that specify the structure of the two nitrogenase components, there is a gene for a factor that is required for component I activity and a gene that codes for a factor possibly involved in electron transport to component II. A mutation in another site does not allow the organism to produce either of the nitrogenase components. All of these genes are co-transducible with the gene that specifics the structure of histidinol dehydrogenase.

Alcohol Oxidoreductases↗
PubMed1975

A systematic approach to enzyme assay optimization illustrated by aminotransferase assays.

We have developed a systematic approach to optimization of reagent concentrations for assays of alanine aminotransferase and aspartate aminotransferase: (a) Michaelis constants describing the initial-velocity kinetics of the coupled enzyme reactions were evaluated by a nonlinear least-squares fit of the appropriate equation to measured enzyme activities. Activities of more than 50 normal and pathological sera were measured at 30 degrees C. (b) These kinetic equations are used to calculate the set of reagent amino- and keto-acid concentrations that all yield a selected fraction of the theoretical maximum enzyme velocity. An optimal pair is determined by defining an additional criterion, such as minimal reagent cost or minimal concentration to Km ratio. (c) The optimum amounts of reagent NADH and coupling enzyme, being a function of desired pre-incubation and measurement intervals, maximum aminotransferase activity to be measured, and endogenous keto-acid concentration, are determined by computer simulation. An approximate relationship and an exact method for computing assay lag time are presented, along with experimentally measured endogenous keto-acid concentrations in serum. All procedures may be applied to other enzyme assays if appropriately modified.

Alanine Transaminase↗
PubMed1974

Simulation of the pentose cycle in lactating rat mammary gland.

A computer model representing the pentose cycle, the tricarboxylic acid cycle and glycolysis in slices of lactating rat mammary glands has been constructed. This model is based primarily on the studies, with radioactive chemicals, of Abraham & Chaikoff (1959) [although some of the discrepant data of Katz & Wals (1972) could be accommodated by changing one enzyme activity]. Data obtained by using [1-(14)C]-, [6-(14)C]- and [3,4-(14)C]-glucose were simulated, as well as data obtained by using unlabelled glucose (for which some new experimental data are presented). Much past work on the pentose cycle has been mainly concerned with the division of glucose flow between the pentose cycle and glycolysis, and has relied on the assumption that the system is in steady state (both labelled and unlabelled). This assumption may not apply to lactating rat mammary glands, since the model shows that the percentage flow through the shunt progressively decreased for the first 2h of a 3h experiment, and we were unable to construct a completely steady-state model. The model allows examination of many quantitative features of the system, especially the amount of material passing through key enzymes, some of which appear to be regulated by NADP(+) concentrations as proposed by McLean (1960). Supplementary information for this paper has been deposited as Supplementary Publication SUP 50023 at the British Museum (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1973) 131, 5.

Animals↗
PubMed1971

A simulation study of brain compartments. Metabolism of glutamate and related substances in mouse brain.

A computer model of the metabolism of glutamate, glutamine, gamma-aminobutyrate, and the tricarboxylic acid cycle in mouse brain has been constructed in terms of 39 reactions among 19 substances or groups of substances (permitting manipulation of 30 independent variables). The model is divided into two compartments, in conformity with previous models based on indirect evidence, and it is found that this compartmentation is indeed the same as that indicated directly with specifically (14)C-labelled acetate and glucose. The movement of materials between the large and small compartments has been studied; glutamine appears to flow from the small to the large compartment, gamma-aminobutyrate in the reverse direction.

Acetates↗