Occurrence of two endoproteinases in wheat leaf intercellular washing fluid

Abstract

The presence of endoproteinases in the intercellular washing fluid of the first wheat (Triticum aestivum) leaf 13 days after sowing was investigated. Two activities were detected after separation of the intercellular fluid proteins by SDS‐PAGE using slab gels containing gelatin as substrate. Their sizes were 70 and 100 kDa. Both enzymes hydrolyzed gelatin and casein. They also seem to be involved in the degradation of a 40 kDa protein component of the intercellular fluid. These results indicate that both enzymes are endoproteinases. They were also obtained from leaves previously sumitted to intercellular fluid extraction. However, the 100 kDa enzyme yield was low, indicating that it is mainly located in the intercellular washing fluid. Assays performed with either specific substrates or inhibitors indicate that both enzymes are serine proteinases.