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The katal (symbol: kat) is that catalytic activity that will raise the rate of conversion by one mole per second in a specified assay system. [1] It is a unit of the International System of Units (SI) [1] used for quantifying the catalytic activity of enzymes (that is, measuring the enzymatic activity level in enzyme catalysis) and other catalysts.
The enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity. [ 1 ] 1 U (μmol/min) is defined as the amount of the enzyme that catalyzes the conversion of one micro mole of substrate per minute under the specified conditions of the assay method .
In biochemistry, a Hanes–Woolf plot, Hanes plot, or plot of / against is a graphical representation of enzyme kinetics in which the ratio of the initial substrate concentration to the reaction velocity is plotted against .
Increasing the substrate concentration increases the rate of reaction (enzyme activity). However, enzyme saturation limits reaction rates. An enzyme is saturated when the active sites of all the molecules are occupied most of the time. At the saturation point, the reaction will not speed up, no matter how much additional substrate is added.
Enzyme activity is commonly used for e.g. liver function tests like AST, ALT, LD and γ-GT in Sweden. [ 5 ] Percentages and time-dependent units (mol/s) are used for calculated derived parameters, e.g. for beta cell function in homeostasis model assessment or thyroid's secretory capacity .
in which e is the concentration of free enzyme (not the total concentration) and x is the concentration of enzyme-substrate complex EA. Conservation of enzyme requires that [28] = where is now the total enzyme concentration. After combining the two expressions some straightforward algebra leads to the following expression for the concentration ...
In enzymology, the turnover number (k cat) is defined as the limiting number of chemical conversions of substrate molecules per second that a single active site will execute for a given enzyme concentration [E T] for enzymes with two or more active sites. [1] For enzymes with a single active site, k cat is referred to as the catalytic constant. [2]
Plasma renin activity (PRA), also known as the renin (active) assay or random plasma renin, is a measure of the activity of the plasma enzyme renin, which plays a major role in the body's regulation of blood pressure, thirst, and urine output. Measure of direct renin concentration (DRC) is technically more demanding, and hence PRA is used instead.