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Biomedical subjects

G L Atkins

Publications and source records attributed to G L Atkins.

At least 19 recordsLinked to original sources
PubMed1991

Developmental changes in the type I procollagen processing pathway in chick-embryo cornea.

Type I procollagen processing in chick-embryo corneas was studied at days 12, 14 and 17 of development. Pulse-chase experiments and electrophoretic analysis of salt-soluble extracts showed developmental changes in the processing pathway. A kinetic model was fitted to the data to determine rate constants for processing of both N- and C-propeptides. Data for pro alpha 1(I)-chain processing and pro alpha 2(I)-chain processing were fitted separately (where pro means procollagen). Between days 12 and 17 the relative flux through the pC-collagen (procollagen chain lacking the N-propeptide) and pN-collagen (procollagen chain lacking the C-propeptide) pathways increased approx. 4-fold. Pro alpha 1(I) chains and pro alpha 2(I) chains were processed by slightly different routes. Variations in the rate constants were compared with electron-microscopic measurements of collagen fibril diameters at each stage of development. Diameters increased by less than 10% over the period from 12 to 17 days. It was concluded that fibril diameters are relatively insensitive to the pathway of procollagen processing in the salt-soluble pool.

Animals↗
PubMed1987

Alternate models for shared carriers or a single maturing carrier in hexose uptake into rabbit jejunum in vitro.

The uptake (tissue accumulation) of three hexoses into rabbit jejunum was measured in a flux chamber in conditions of effective stirring. Glucose uptake was inhibited by galactose or 3-O-methylglucose: 1-40 mM galactose caused a progressive decline in glucose uptake; 1-5 mM 3-O-methylglucose inhibited glucose uptake but higher concentrations of 3-O-methylglucose had no further effect. When 1-40 mM 3-O-methylglucose was added to glucose plus galactose there was a further decrease in the uptake of glucose; adding 1-40 mM galactose to glucose plus 3-O-methylglucose also produced a decrease in glucose uptake. Both glucose and 3-O-methylglucose inhibited uptake of galactose but the pattern of inhibition varied between the two sugars. The uptake of 3-O-methylglucose was also inhibited by glucose and by galactose, but the uptake of 3-O-methylglucose in the presence of either galactose or glucose was no further reduced by adding the third hexose. Graphical analysis and analysis by non-linear regression both showed that neither the single Michaelis-Menten function, nor the single Michaelis-Menten-plus-competitive-inhibition function was appropriate for any of these data. The results are consistent with the hypothesis that either there are multiple (at least three) intestinal carriers for hexoses; alternatively that there is a single carrier whose transport properties for the three hexoses change differentially during cell maturation and migration up the villus.

3-O-Methylglucose↗
PubMed1985

Nonlinear regression on a microcomputer: which program?

Eleven published programs for performing nonlinear regression using a microcomputer have been reviewed. They have been assessed according to many criteria, especially: application, program language, algorithm used, method for calculating partial differentials, facility for weighting, desirable input and output features, robustness during execution, memory requirements, accessability, ease of implementation and evaluation and testing. No one program contains all the desirable characteristics discussed, but guidance is given as to which might be the most suitable for a particular purpose or for a given microcomputer system.

Algorithms↗
PubMed1985

The economic status of the oldest old.

Proposals to shift more of Medicare's costs to beneficiaries raise the question of whether the oldest old--the heaviest users--have the resources to bear these costs. Information on cash income, assets, other economic resources, and in-kind benefits provides an assessment of the economic status of the very old. When all factors and adjustments are considered, the oldest old, as a group, are shown to have substantially lower economic status than the young old.

Aged↗
PubMed1977

The computation of saturable and linear components of intestinal and other transport kinetics.

1. Published data for absorption kinetics have been fitted by non-linear regression to (i) a single Michaelis-Menten function, (ii) a Michaelis-Menten function plus a linear term and (iii) a sum of two Michaelis-Menten functions. A series of criteria have been drawn up to establish the goodness of fit in each case. 2. In 17 out of 35 cases the Michaelis-Menten function was the "best fit". In nine cases the "best-fit" model also included a linear term, but never was the sum of two Michaelis-Menten functions accepted to be the "best-fit" model. 3. Linearity of a Lineweaver-Burk plot was of unreliable diagnostic value in assessing goodness of fit. 4. Since the fit of a Michaelis-Menten function was often poor, simulated data sets with error were used to study the influence of experimental design etc. on Michaelis-Menten parameter estimation. 5. Precision of estimation of Km is increased by increasing the number of data points, reducing their variance, increasing the data range and by straddling Km in the observations. For a given constant number of observations there is no advantage in using replicate observations at few concentrations or single values at relatively many concentrations, or in using single values rather than means. 6. The caution necessary in interpretation of kinetic models is emphasized.

Animals↗
PubMed1977

An evaluation of ways of using equilibrium dialysis to quantify the binding of ligand to macromolecule.

1. The effect of systematic error (loss of ligand, complex or macromolecule) on three of the experimental designs by which equilibrium dialysis may be used to quantify the interaction of ligand and macromolecule is examined theoretically, and the design that is least sensitive to systematic error is identified. 2. Thirteen methods for fitting the binding isotherm to experimental data are compared by using them to analyse simulated data containing random error, and the most reliable method is identified.

Dialysis↗
PubMed1976

Methods for fitting equations with two or more non-linear parameters.

1. Descriptions are given of two ways for fitting non-linear equations by least-squares criteria to experimental data. One depends on solving a set of non-linear simultaneous equations, and the other on Taylor's theorem. 2. It is shown that better parameter estimates result when an equation with two or more non-linear parameters is fitted to all the sets of data simultaneously than when it is fitted to each set in turn.

Enzymes↗
PubMed1975

A comparison of seven methods for fitting the Michaelis-Menten equation.

The Michaelis-Menten equation was fitted to simulated data containing different sorts of error by using the three linear transformations, and the methods of S. R. Cohen [Anal. Biochem. (1968) 22, 549-552], R. Eisenthal & A. Cornish-Bowden [Biochem. J. (1974) 139, 715-120], F. de M. Merino [Biochem. J. 143, 93-95] and G. N. Wilkinson [Biochem. J. (1961) 808 324-332). The best methods were those of Eisenthal & Cornish-Bowden (1974) and Wilkinson (1961).

Kinetics↗
PubMed1974

Weighting functions and data truncation in the fitting of multi-exponential functions.

Artificial data were simulated by using two-exponential functions and normally distributed pseudo-random numbers. The variation corresponded to either constant or relative variance for the data error. These data were used to test (i) three different weighting functions and (ii) the effect of data truncation on the precision of estimating the parameters of two-exponential functions.

Analysis of Variance↗
PubMed1974

A comparison of two methods for fitting the integrated Michaelis-Menten equation.

The methods of Atkins & Nimmo (1973) and Fernley (1974) for fitting the integrated Michaelis-Menten equation were compared by using the same sets of simulated experimental data. The method of Fernley (1974) is to be preferred because it gives precise and unbiased estimates of the Michaelis-Menten parameters over a wide range of substrate concentrations. However, the estimates may not be symmetrically distributed, especially at low substrate concentrations.

Catalysis↗