Proteolytic activity in the maize pollen wall

Abstract

A new protease from maize ( Zea mays L.) pollen is described. It was purified using gel filtration, ion exchange and high performance liquid chromatography. SDS‐PAGE and HPLC showed that the enzyme has a dimeric structure of M, ca 60,000. Inhibitor investigations indicated an aspartic acid residue in its active site. The optimum pH for maize pollen aspartic proteinase activity was 5.6, and the optimum temperature was 45°C. The enzyme is easily eluted from the pollen grains and, as confirmed by enzymoblotting after isoelectric focusing, it is located in the pollen wall. Similar to metallo‐proteinases, its activity is inhibited by Zn 2+ . The pL value for purified aspartic proteinase, as estimated after IEF, was 5.0. Two‐dimensional electrophoresis analysis of proteins eluted from maize pistils suggests that the enzyme digests the proteins and may be involved in pollen‐tube germination. The properties of serine and aspartic proteinases from maize pollen are compared.