On the properties of the international standards for tissue plasminogen activator

During the last four and a half years, several preparations of human single-chain tissue plasminogen activator (tPA) from melanoma cell cultures (1) were made. These preparations were analysed for homogeneity, protein content, fibrinolytic activity and amidolytic activity. Because of concern with increasing specific fibrinolytic activity, I investigated the effects of various solvents and the stability of the 2nd International Standard at room temperature