Abstract
In pelagic egg-spawning marine fish, hepatically derived vitellogenin undergoes limited proteolysis within the follicles during early oocyte maturation followed by additional degradation during late oocyte maturation. This study demonstrates the role of cathepsin D expressed in late maturating oocytes of round scad Decapterus maruadsi, in relation to ovarian cathepsins B and L that are possible agents causing yolk degradation. Ovarian cathepsins B, D and L in late oocyte lysate were isolated by gel filtration, and their respective molecular masses were estimated as 26.7, 34.9 and 29.9 kDa. The effect of pepstatin, a potent inhibitor of cathepsin D, was examined on their activities in the oocyte lysate and isolates of cathepsins. In both sources, the activity of cathepsin D was completely inhibited whereas that of cathepsin L was not inhibited. However, the activity of cathepsin B in the lysate was significantly reduced while no inhibition of its activity was observed in the isolate. Results indicate that ovarian cathepsin D is involved in activation of coexistent procathepsin B during late oocyte maturation in scad.
