Study of the nature of lysosomes and of their acid phosphatase

Abstract

Treatment with M/2 CaCl2 or fresh frozen sections of various organs of mice inhibits the subsequent histochemical demonstration of acid phosphatase by various procedures. This inhibition can be reversed by treatment with M/I NaCl. Fixation in cold formalin solution, or treatment with fat solvents weakens or abolishes this effect with the result that phosphatase staining is not markedly influenced by pretreatment with salts. The effect of surfactants in inhibiting acid phosphatase staining is diminished by fixation in formalin. Treatment with M/2 CaCl2 of fresh frozen sections of mice organs partly inhibited the histochemical staining of phospholipids. The findings indicate that acid phosphatase molecules are bound to polar lipids and that under the influence of excess of Ca ions the lipoproteic molecules of acid phosphatase form droplets bounded by hydrophobic groups of the lipids. In such droplets the enzyme molecules are not available to act on substrates dissolved in the medium, and the droplets may be regarded as lysosomes. Under the influence of excess Na ions in the milieu the lipoprotein layer breaks into droplets bounded on the outside by the enzyme protein and the hydrophilic groups of the phospholipids. Such particles probably represent microsomes. The implications of these conclusions are discussed.