Serum collagenase-like peptidase activity in rheumatoid arthritis and systemic lupus erythematosus.

Collagenase-like (CL) peptidase activity in serum, which was measured using a newly synthesized substrate, (succinyl-Gly-Pro-Leu-Gly-Pro)-4-methylcoumaryl-7-amide, was significantly lower in patients with advanced rheumatoid arthritis or with systemic lupus erythematosus than that in normal controls. Decrease of the serum enzyme activity was more pronounced in systemic lupus erythematosus. No significant change in serum CL-peptidase activity was found in other connective tissue diseases such as mixed connective tissue disease and Sjögren's syndrome.