Protein was determined based on the method described by
Bradford (1976), using ovalbumin as a standard. General proteolytic
activity was determined with two different substrates: 0.5%
(w/v) fluorescein isothiocyanate-labeled (FITC) casein (casein-
FITC) (fluorescent substrate, useful at pH values above 5) or 0.5%
hemoglobin-FITC (fluorescent substrate, useful at pH values below
4.5). The preparation of the substrates and the assays was based on
the method described by Twining (1994) in 50 mMsodium citratephosphate
buffer at pH 5.5 with casein-FITC or in the same buffer at
pH 3.5 with hemoglobin-FITC as substrate.