Do serine proteases degrade amyloid A fibrils?

Human serum contains enzyme(s) able to degrade serum amyloid A protein (SAA) and amyloid A (AA) fibrils. On the basis of inhibition tests these enzymes are regarded as serine proteases, but further characterization of the enzymes has, however, so far not been done. Chymotrypsin, trypsin, elastase, collagenase and kallikrein, when added to SAA-containing serum, all degraded SAA to peptides within 2 h at 37 degrees C. With the exception of collagenase these enzymes also destroyed the Sirius-Red-binding ability of amyloidotic tissue and that of isolated AA fibrils. Hence, they altered the conformation of the beta-pleated structure and possibly also degraded the fibrils. These results suggest that any of these serine proteases could be responsible of the degradation of SAA in serum. The enzyme concentrations needed to degrade amyloid fibrils, however, were much higher than normally found in serum. Thus, it is unlikely that the amyloid-fibril-degrading activity in serum could be due to any of these enzymes.