Acid protease and its Proenzyme from Human Seminal Plasma

Abstract

An acid protease with an optimum pH of 2.5 was first described in human seminal plasma as pepsin and pepsinogen (1), but had not been purified or characterized. Recently, we have purified the acid protease and its proenzyme from human seminal plasma (2,3). In many respects, the properties of seminal plasma acid protease are similar to those of gastric pepsin. Since the proenzyme is more stable than the active enzyme in alkaline solution and can be converted into its active form in acidic solution, the acid protease is likely to exist in seminal plasma, at the physiological pH around 7.5 (4), in proenzyme form.