The Structure and Function of Acid Proteases

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Abstract
The distribution of acid protease activity in various tissues of Japanese monkey (Macacafuscata fuscata) was investigated with hemoglobin as a substrate at pH 3.0. The activity per protein weight in crude extracts was highest in spleen and lung, and decreased in the order: spleen, lung>kidney, testis>brain>liver, placenta>thyroid gland, muscle. The activity in crude muscle extract was about one-tenth those of spleen and lung. The activity per wet tissue weight was in roughly the same order except for a lower activity per wet weight of brain. Upon chromatography of each crude extract on a Sephadex G-100 column, one major activity peak was eluted at a position corresponding to a molecular weight of about 41,000. This enzyme activity is attributed to cathepsin D [EC 3.4.23.5]. In addition, a minor activity peak was eluted in the case of spleen, lung and kidney at the break-through position, corresponding to a molecular weight of more than 100,000. This activity peak is presumably due to cathepsin E. These acid protease activities were, in most cases, strongly inhibited by pepstatin, an acid protease-specific peptide inhibitor. The distribution of acid protease activity was investigated in the brain of crab-eating monkey (Macaca fascicularis). The activity was fairly evenly distributed among several regions of the brain, and its distribution was similar to those of other acid hydrolases, especially N-acetyl-β-D-glucosaminidase [EC 3.2.1.30] and acid phosphatase [EC 3.1.3.2], which are marker enzymes of lysosomes.