Extracellular fluid proteins of goldfish brain: evidence for the presence of proteases and esterases

: Preparations of enriched fractions of extracellular fluid (ECF) proteins from goldfish brain were found to contain protease(s) and esterase(s). The N-substituted furanacryloyl (FA) peptides FA-Phe-Gly-Gly and FA-Phe-OMe were used as model substrates for determining protease and esterase activity, respectively, in a spectro-photometric assay. Studies of the profile of substrate specificity and identification of the types of compounds that were effective as inhibitors showed that these ECF enzymes have some distinctive properties. GSH, but not GSSG, and EDTA inhibited the protease(s) without influencing the esterase(s), whereas l-1-tosylamide-2-phenylethylchloromethyl ketone blocked both protease and esterase activites of ECF. Most of the protease and esterase properties of ECF could be bound to concanav-alin A-Sepharose affinity chromatographic columns in association with ependymin—a brain extracellular protein. These observations indicate that ECF may contain a metalloprotease(s) and raise the possibility that the ependymins might be a substrate for these ECF enzymes.