The synthetic substrate 6-nitro-3-(phenylacetamido) benzoic acid (NIPA
B) is an appropriate substrate for assaying penicillin acylase activit
y in reversed micellar systems of Aerosol - OT in isooctane. Accumulat
ion of 6-nitro-3-aminobenzoic acid (NABA) produced by the enzymatic hy
drolysis of NIPAB, followed by the increase in absorbance at 405 nm, w
as linear at 4 to 20 mM for up to 30 minutes and 15 degrees C to 40 de
grees C.