(one unit is the amount of enzyme required to convert 1 μmol of G3 CNP) was prepared. All of the solutions were prepared in 20 mM phosphate buffer pH 7.0 containing 10 mM NaCl and 15% (v/v) glycerol. The mixture was incubated at 37 1C and the absorbance of the CNP produced was measured at 405 nm every 5 s throughout 60 s.