Hypothalamic cathepsin D: assay and isoenzyme composition.

A sensitive and convenient method of endopeptidase assay using as substrate globin modified with pyridoxal-5-phosphate was used for determination of acid proteinases in bovine hypothalamus separated by isoelectric focusing. The soluble protein fraction of hypothalamus upon elution from Sephadex gave five peaks of proteinase activity at pH 3.2. The properties indicate that these peaks of endopeptidase activity are isoenzyme forms of cathepsin D.