Utility of combining MMP-9 enzyme-linked immunosorbent assay and MMP-9 activity assay data to monitor plasma enzyme specific activity.

The aim of this study was to combine matrix metalloproteinase-9 (MMP-9) protein (enzyme-linked immunosorbent assay [ELISA]) and MMP-9 activity (fluorescence resonance energy transfer [FRET] assay) data to generate units of specific activity in endogenous and p-aminophenylmercuric acetate (APMA)-activated lithium heparin plasma. The results indicate that specific activity is constant in APMA-activated plasma (mean value=1359.4 pmol/min/microg) and approximately 12% plasma MMP-9 is endogenously active. Exogenous tissue inhibitor of metalloproteinase-1 (TIMP-1) has a greater inhibitory effect on endogenously active MMP-9 than on APMA-activated MMP-9. In conclusion, specific activity can be used as a tool to monitor MMP-9 inhibition. APMA activation affects natural enzyme inhibition, possibly by chemical modification of the C-terminal portion of the enzyme containing the TIMP-1 binding site.