Immunochemical difference between cathepsin D and cathepsin E-like enzyme from rat spleen.

The immunological properties of acid proteinases from rat spleen, two types of cathepsin D and a cathepsin E-like enzyme, were examined. The rabbit antiserum was prepared against the major form of cathepsin D (cathepsin D-I) from rat spleen. The antiserum quantitatively precipitated the enzyme activity from the purified cathepsin D-I preparation. On immunodiffusion analysis, the antiserum showed an identical reaction with the minor form of cathepsin D (cathepsin D-II) from rat spleen. Immunoelectrophoresis showed that the precipitin line with cathepsin D-II ran somewhat faster to the anode than that with cathepsin D-I. The cathepsin E-like acid proteinaspe was neither precipitated nor inhibited by the antiserum to cathepsin D-I, indicating that the cathepsin E-like enzyme is different from cathepsin D. Immunological gel diffusion with the antiserum indicated that rat spleen cathepsin D was immunologically identical with cathepsin D obtained from rat brain, thymus, lungs, heart, liver, kidneys, and adrenals.