The affinity of the cofactor will also influence whether a compound that competes

with cofactor binding can be identified. The effects that exogenous cofactor have on biochemical enzyme assays can often be treated like substrate addition – PARP inhibitor cancer the amount required depends on the level of activity needed and the necessity of the cofactor for the enzyme form one chooses to inhibit. In general, if additional cofactor is required to obtain a robust enzyme assay, then it is usually best to use a saturating concentration in the assay when not specifically screening for cofactor-competitive compounds. Titrations of the cofactor should also be performed to identify the best possible signal:background ratio and to ensure that the reaction is not inhibited at high concentrations of cofactor. Cofactors can also interfere with product detection depending on the method used and therefore the necessity for cofactors may ultimately dictate which detection technique can be applied to a particular target. Finally, stability of a cofactor needs to be considered for the time and environment that the cofactor will be exposed to during an HTS run. For example, some cofactors are light sensitive (iron guanylyl pyridinol) while others can change redox state in common buffers without reducing agents (iron salts). The timing of these modifications must be considered and tested to assure compatibility with the HTS process. Typically,

in vitro biochemical assays are performed at near physiological pH in an attempt to mimic the intracellular environment of the native enzyme. Most enzymes will show broad pH sensitivity due to denaturation click here at high/low pH or to protonation/deprotonation of residues directly involved in acid-base chemistry. For cytosolic proteins, pH≈7.4 can be maintained by a number of buffers including Tris, HEPES, MOPS, and sodium or potassium phosphate buffers, to name a few. However simply because an enzyme is found in the cytosol does not guarantee that the

activity will be optimal at pH=7.4. Monoiodotyrosine A range of pH values encompassing pH=7.4 should be tested in enzymatic activity assays, taking into account that differences in the local environment in vitro versus in vivo or changes in the protein construct from the native form could alter the optimum pH for reactivity. However diverging too far from physiological pH in a biochemical assay can alter the interaction between the enzyme and compounds, creating a potential disconnect between the biochemical and cellular activity of these compounds. The choice of buffer can also have significant consequences for a biochemical reaction because each buffer can have unique and significant effects on a given enzyme target. In addition, necessary reaction components can interact poorly with certain buffers, resulting in non-optimal assay conditions and affecting the robustness and reproducibility of an assay.