An improved spectrophotometric assay for human plasma carboxypeptidase N

A continuous spectrophotometric assay for human plasma carboxypeptidase N utilizing furylacryloyl-alanyl-lysine is described. Synthesis was made by use of 9-(2-sulfo)fluorenylmethyloxycarbonyl (Sulfmoc) chloride as the N-?-amino-blocking group for lysine. The substrate has the advantage of containing a chromophore which allows difference measurements above 324 nm. The kinetic parameters K_m and $\text{K}{}_{\mathrm{<mtext>cat</mtext>}}\text{K}{}_{\mathrm{m}}$ have been determined for furylacryloyl-alanyl-lysine and -arginine. Difference measurements were related to micromoles of lysine or arginine released and were expressed as units.