Immunochemical Difference between Cathepsin D and Cathepsin E-Like Enzyme from Rat Spleen

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Abstract
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-1) from rat spleen. The antiserum quantitatively precipitated the enzyme activity from the purified cathepsin D-I preparation. On immuno-diffusion analysis, the antiserum showed an identical reaction with the minor form of cathepsin D (cathepsin D-1l) 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 proteinase 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.