Abstract: A crude membrane fraction of leaf sheath tissue of a grass endophytically infected by A. typhinum is produced. The extract exhibits endoproteolytic activity in the presence of detergent or after methanol precipitation. This activity is optimal at 35.degree.-40.degree. C. and pH 10-11 and is exhibited only when a reductant is present. The activity is associated with a first gel electrophoresis band having apparent molecular weight of 205,000 daltons when said extract is electrophoresed without prior boiling; however, when said extract is boiled prior to electrophoresis, there results a band having apparent molecular weight of 34,000 daltons. This band gives rise to polyclonal rabbit antibodies which are not cross react with proteinase K. The preferred source of Acremonium typhinum is ATCC 74228.