Neutral Proteases Confined to One Class of Lysosomes of Human Polymorphonuclear Leukocytes

We find that protease and esterase activity of human PMN exist in a latent form in a class of membrane-bound particles which sediment at a distinctive density. Readily separated from these granules by sucrose density gradient centrifugation is a separate class of particles, which is associated with an aminopeptidase not previously described in human PMN lysosomal granules. Protease, esterase, and aminopeptidase act optimally at or near pH 7.2.