Biochemical assays are based on the chemical action of a biopharmaceutical which mimics the biological function. A good example of such an assay is that for tissue plasminogen activator (TPA) in which the biological function of TPA (lysing of blood clots) is mimicked by the addition of TPA and plasminogen to a synthetic fibrin clot [58, 59], The time required for lysis of the synthetic clot by plasmin produced by TPA's activation of plasminogen is measured by spectrophotometry. Because the measured parameter is a chemical signal, the precision of this type of assay is quite good. It is also amenable to automation, relatively inexpensive and simple to execute when compared with bioassays. However, the most important criteria for the validity of such an assay is its accuracy in mimicking the biological function and its sensitivity to the presence of protein variants in the sample. This would require comparison of the results of this assay against a valid whole animal or cell culture based bioassay as well as measure its response to authentic structural variants of the target protein.
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