Abstract
Summary
Rat tissues have been fractionated in order to assay their plasminogen activator activity. Mitochondria, microsomes, and the final supernate separated from rat liver were essentially equal in this activity suggesting that the soluble plasminogen activator in the cell homogenate had equilibrated among them. Lysosomes showed significantly greater plasminogen activator activity than the other fractions. The plasminogen activator release from lysosomes could be increased by sonification and freezing and thawing. When the lysosomes of a series of six tissues were compared, lung lysosomes were richest in plasminogen activator. The activator activity was approximately the same for lysosomes of rat spleen, kidney, liver, brain, and lymph node. Proteolytic activity of rat liver cell fractions was less than 1/4 that measured in the presence of plasminogen. Fibrinolytic activity of cell fractions measured with heated fibrin clots was negligible.
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