enzyme assays are used to measure the activity of an enzyme.
enzyme assays are used to measure the activity of an enzyme.
what methods are used to measure the activity of an enzyme?
enzyme assays
enzyme assays are laboratory procedures that measure the rate of enzyme reactions. since enzymes are not consumed by the reactions they catalyse, enzyme assays usually follow changes in the concentration of either substrates or products to measure the rate of reaction. there are many methods of measurement. spectrophotometric assays observe change in the absorbance of light between products and reactants; radiometric assays involve the incorporation or release of radioactivity to measure the amount of product made over time. spectrophotometric assays are most convenient since they allow the rate of the reaction to be measured continuously. although radiometric assays require the removal and counting of samples (i.e., they are discontinuous assays) they are usually extremely sensitive and can measure very low levels of enzyme activity. an analogous approach is to use mass spectrometry to monitor the incorporation or release of stable isotopes as substrate is converted into product.
enzyme kinetics
bullet::::- glutathione reductase is a nicotinamide adenine dinucleotide phosphate (nadph) and fad-dependent enzyme, and the major flavoprotein in erythrocytes. the measurement of the activity coefficient of erythrocyte glutathione reductase (egr) is the preferred method for assessing riboflavin status. it provides a measure of tissue saturation and long-term riboflavin status. in vitro enzyme activity in terms of activity coefficients (ac) is determined both with and without the addition of fad to the medium. acs represent a ratio of the enzyme’s activity with fad to the enzyme’s activity without fad. an ac of 1.2 to 1.4, riboflavin status is considered low when fad is added to stimulate enzyme activity. an ac  1.4 suggests riboflavin deficiency. on the other hand, if fad is added and ac is  1.2, then riboflavin status is considered acceptable. tillotson and bashor reported that a decrease in the intakes of riboflavin was associated with increase in egr ac. in the uk study of norwich elderly, initial egr ac values for both males and females were significantly correlated with those measured 2 years later, suggesting that egr ac may be a reliable measure of long-term biochemical riboflavin status of individuals. these findings are consistent with earlier studies.
riboflavin