Acid protease active in intracellular protein breakdown. In chicken it is a key enzyme for yolk formation as it is capable of catalyzing intra oocytic break down of protein components of both vitellogenin and VLDL. Specificity similar to, but narrower than, that of pepsin A. Does not cleave the 4-Gln-|-His-5 bond in B chain of insulin. Consists of a light chain and a heavy chain. Oocytic yolk, preovulatory follicles, liver. Belongs to the peptidase A1 family.