Low molecular weight proteinase inhibitors. I. Extraction and identification of activity from normal and malignant human breast tissues.

Extracts of both normal human breast tissues and infiltrating ductal carcinoma tissues were ultrafiltered and concentrated to recover proteins having nominal molecular weights between 1000 and 50,000 daltons. Proteinase inhibitory activity of the final concentrates of tumours and normal breast controls were found to be distinct from the majority of proteinase inhibitory activity in human serum as judged by cellulose acetate electrophoresis. All final concentrates contained proteinase inhibitory activity with electrophoretic mobilities similar to that of Trasylol. Molecular sieve chromatography on high performance liquid chromatographs of the final concentrate of a tumour extract containing the greatest proteinase inhibitory activity indicated that the activity was present within 2 peaks having apparent molecular weights of 22,000 and 7000 daltons.