Proteolytic Activity in the Seminal Plasma of the Mud Crab, Scylla serrata (Forskal)

Abstract

The protein composition and proteolytic activity of the seminal plasma of the brachyuran crab, Scylla serrata, were studied. The seminal plasma proteins are mainly glycoproteinaceous, many of them lying in the lower molecular weight range as evidenced by high performance liquid chromatography (HPLC). Protease activity was detected using casein as the substrate. The enzyme was highly active in the pH range 7.0–9.0, exhibiting maximum activity at pH 8.0. The enzyme was active at temperatures up to 40°C. Enzyme activity was inhibited by the serine protease inhibitor Phenyl Methyl Sulfonyl Fluoride (PMSF) but not by the metalloprotease inhibitor Ethylene Diamine Tetra Acetic acid (EDTA) indicating that it is a serine protease. The effect of substrate concentration on the enzyme activity was also studied. The proteins were fractionated by gel filtration chromatography on Sephadex G-200 column. A clear zone of proteolysis was detected against a stained background in the third fraction when electrophoresed on casein-containing polyacrylamide gel. The molecular weight of this fraction was determined to be approximately 6000D. The protease activity in the seminal plasma may be related to the formation and/or dissolution of sperm plug formed during mating in these brachyuran crabs.