Patent ID: 7338774

Claim:
A method for calculating activity of a cyclin-dependent kinase in a sample prepared from a living cell comprising the steps of: catching the cyclin-dependent kinase in the sample by anti-cyclin-dependent kinase antibody; reacting an adenosine 5′-O-(3-thiotriphosphate) (ATP-γS) with a substrate for the cyclin-dependent kinase in presence of the cyclin-dependent kinase in order to introduce a monothiophosphate group into a serine or threonine residue of the substrate, the substrate not containing a sulfur atom; coupling a labeling fluorophore or a labeling enzyme with a sulfur atom of the introduced monothiophosphate group of the substrate in buffer solution; adding a thiol to the buffer solution to stop the coupling between the sulfur atom and the labeling fluorophore or the labeling enzyme; measuring an amount of fluorescence from the labeling fluorophore, or reacting the labeling enzyme with a substance to generate an optically detectable product and measuring an amount of the generated product; and calculating the activity of the cyclin-dependent kinase from the measured amount of fluorescence or the measured amount of the generated product with reference to a pre-produced reference curve.