Serum glycylproline p-nitroanilidase activity in rheumatoid arthritis and systemic lupus erythematosus.

Glycylproline p-nitroanilidase activity in serum of patients with advanced rheumatoid arthritis or with systemic lupus erythematosus but with normal hepatic function was found to be significantly lower than that of normal adult controls. Decrease of this enzyme's serum activity was more pronounced in systemic lupus erythematosus. A significant inverse correlation was observed between the enzyme activity and the duration of rheumatoid arthritis.