Patent ID: 7452690

Claim:
A method for determining target protease activity in a sample, employing a transfected cell comprising a hindered protein reagent, said hindered protein reagent comprising a membrane bound protein component bound to a cell membrane surface, said protein component linked to an enzyme donor fragment of β-galactosidase by a recognition sequence of from 4 to 12 amino acids susceptible to cleavage by said target protease activity to produce an enzyme donor fragment, said cell surface of said hindered protein reagent inhibiting the formation of a complex between said enzyme donor fragment of β-galactosidase and a partner enzyme acceptor fragment of β-galactosidase resulting in a low background signal, wherein cleavage produces a protein reagent fragment active with said enzyme acceptor fragment of said β-galactosidase to produce an active β-galactosidase enzyme resulting in an increase in β-galactosidase enzyme activity, wherein β-galactosidase enzyme activity is related to said target protease activity, said method comprising: combining said transfected cell, said sample, enzyme acceptor fragment of β-galactosidase and β-galactosidase enzyme substrate for a time sufficient for said target protease activity to cleave said recognition sequence; and measuring the β-galactosidase enzyme activity as an indication of the protease activity.