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Biomedical subjects

L Theodorsen

Publications and source records attributed to L Theodorsen.

At least 55 records · Page 3Linked to original sources
PubMed1982

Application of response surface methodology to the assay of gamma-glutamyltransferase.

Response surface methodology (RSM) offers an empirical approach to the study of clinical enzyme assays. Variables such as pH, which are difficult to characterize by using theoretical enzyme kinetics, are easily included in RSM formulations. In this investigation, we studied with RSM the change in the measured activity of gamma-glutamy-transferase (EC 2.3.2.2) as a function of changes in concentrations of donor (gamma-glutamyl-3-carboxy-4-nitroanilide) acceptor (glycylglycine), and pH. The study defined large ranges for these variables over which maximum enzyme activity is obtained: donor 6.6 to 10.2 mmol/L, acceptor 129 to 250 mmol/L, and pH 7.8 to 8.5. The RSM regression polynomial was as accurate as a previously determined enzyme kinetic equation for predicting the transferase activity from given reagent substrate concentrations. Although not yielding a mechanistic understanding of an enzyme assay, RSM studies do produce an operational understanding of how an assay functions.

Clinical Enzyme Tests↗
PubMed1981

gamma-Glutamyltransferase in human serum: an analysis of kinetic models.

The purpose of the study was to elucidate details of the kinetic model for gamma-glutamyltransferase when assayed with gamma-glutamyl-3-carboxy-4-nitroanilide and glycylglycine as substrates. Data from several sets of initial velocity measurements were fitted by nonlinear regression to a set of different kinetic models. gamma-Glutamyltransferase acts by a "ping-pong bi-bi" mechanism. A model encompassing transfer and autotransfer, competitive inhibition by the acceptor substrate, and no inhibition by the donor substrate gives the best fit to the experimental data. Effects of spectrophotometric nonlinearity may simulate noncompetitive inhibition by the donor substrate. The nonlinearity is dependent on the absorption of the incubation mixture and therefore is related to the concentration of the donor substrate and the wavelength (405-412 nm) used to monitor the reaction. With decreasing pH the autotransfer fraction decreases and the binding of the donor substrate to the acceptor site increases, simulating an increased competitive inhibition by the donor substrate. These results are of importance when elaborating optimum assay conditions for gamma-glutamyltransferase in serum.

Humans↗
PubMed1978

The significance of bone marrow acid phosphatase in patients with prostatic carcinoma.

The levels of total and l-tartrate labile acid phosphatase were studied in 49 patients with prostatic carcinoma. The results were compared with the results from a control group. The acid phosphatase levels from the bone marrow were above the upper normal limit of serum acid phosphatase both in the control group and in patients with prostatic carcinoma. This may be due to acid phosphatase released from blood cells during haemolysis. There was a positive correlation between serum and bone marrow acid phosphatase levels in patients with prostatic carcinoma. Significantly raised levels of bone marrow acid phosphatase (above the upper limit of the normal range from the control group) were observed only in advanced stage IV patients with significantly increased serum levels. The levels of bone marrow acid phosphatase gave no supplementary diagnostic information in any of the patients with prostatic carcinoma. Doubt is expressed concerning the hypothesis that raised levels of bone marrow acid phosphatase are diagnostic of early metastases from prostatic carcinoma.

Acid Phosphatase↗
PubMed1977

Twenty-four hour variation in flow and composition of leg lymph in normal men.

The twenty-four hour variation in concentration and output of total protein, lactate dehydrogenase and alkaline phosphatase has been studied in the peripheral lymph from the legs of 5 healthy volunteers over a period of five days. The highest concentration of these proteins was found in lymph collected during the first two hours after a night's rest. During the day a continuous decrease in concentration occurred without any direct correlation to lymph flow. The variation in lymph protein concentration between early morning and late day was about 40%, lactate dehydrogenase and alkaline phosphate about 90% and 45% respectively.

Adult↗
PubMed1977

Flow and composition of leg lymph in normal men during venous stasis, muscular activity and local hyperthermia.

Changes in normal human leg lymph protein concentration, output, and lymph flow/lymph protein concentration relationship, as well as lactate dehydrogenase and alkaline phosphatase activity were followed during procedures known to increase capillary filtration as venous stasis, muscular exercise and warming of tissues. Lymph flow increased by 83% during two hour ergometer cycling, and by 117% during two hour warm water foot bath. During a two hour period of venous stasis lymph flow dropped by 50%. There was an increase in lymph flow during the rest period following all three types of experiment, most pronounced after foot warming. An inverse relationship between the lymph flow rate and lymph protein concentration was found. Lymph enzymes followed the same pattern of changes as total protein.

Adult↗
PubMed1976

Gamma-Glutamyl-3-carboxy-14-nitroanilide: the substrate of choice for routine determinations of gamma-glutamyl-transferase activity in serum?

Gamma-Glutamyl-3-carboxy-4-nitroanilide has been tested as donor substrate in the assay of gamma-glutamyltransferase activity in serum, glycylglycine being used as acceptor substrate. This donor substrate is highly solube even in neutral solutions, in contrast to the commonly used gamma-glutamyl-4-nitroanilide. The enzyme which apparently acts accordingly to a ping-pong bi bi kinetic mechanism, shows an absolute KM value for gamma-glutamyl-3-carboxy-4-nitroanilide of about 0.64 mmol/l, and for glycylglycine of about 13.4 mmol/l. The former KM value is significantly lower than that previously found for gamma-glutamyl-4-nitroanilide. The carboxyl derivative exhibits a marked competitive inhibitory effect on the gamma-glutamyltransferase. This effect is more pronounced than that of gamma-glutamyl-4-nitroanilide. The carboxyl derivative has somewhat higher absorbance in the range of wave length (400-420 nm) used to monitor the formation of the product. It is concluded that as donor substrate in the assay of gamma-glutamyltransferase activity of serum, the new derivative is not substantially superior to the gamma-glutamyl-4-nitroanilide conventionally used.

1-Carboxyglutamic Acid↗
PubMed1976

Gamma-glutamyltransferase: Substrate inhibition, kinetic mechanism, and assay conditions.

Gamma-glutamyltransferase activity in serum is shown to be competitively inhibited by the two substrates gamma-glutamyl-4-nitroanilide and glycylglycine. Awareness of this is of importance when one is choosing final reaction conditions for the assay of the enzyme. Gamma-glutamyltransferase probably acts by a "ping-pong bi-bi" kinetic mechanism, which fits with the double competitive substrate inhibition demonstrated. The product, 4-nitro-aniline, appears to be an uncompetitive dead-end inhibitor of both substrates. Various amino acids, particularly glycine and L-alanine, inhibit the enzyme. Their inhibition patterns are uncompetitive with glycylglycine and competitive with gamma-glutamyl-4-nitroanilide. On the basis of the present and other studies, the Scandinavian Society for Clinical Chemistry and Clinical Physiology is going to recommend for routine use a gamma-glutamyltransferase method in which the final concentrations of gamma-glutamyl-4-nitroanilide and glycylglycine are 4 and 75 mmol/liter, respectively.

Amino Acids↗