A PROBARLEY LECTIN PROCESSING ENZYME PURIFIED FROM ARABIDOPSIS-THALIANA SEEDS

An aspartic proteinase was purified from the seeds of Arabidopsis thal iana (ecotype RLD) using affinity chromatography on pepstatin-agarose and ion exchange chromatography. The purified enzyme is optimally acti ve at pH 3.5 and completely inhibited by pepstatin A. The purified Ara bidopsis aspartic proteinase contains four subunits (apparent molecula r weights 31, 28.5, 15 and 6 kDa), two of which are probably linked by disulfide bridges. These properties are similar to the aspartic prote inase previously isolated from barley seeds. The amino acid sequence o f the peptide subunits corresponds exactly with the sequence of the pr eviously isolated cDNA for the Arabidopsis aspartic proteinase. The Ar abidopsis enzyme processed probarley lectin in vitro at the carboxy-te rminus between phenylalanine and alanine, the same place where the bar ley enzyme cleaves the lectin in vitro. The aspartic proteinase appear s to be the major enzyme processing the lectin in seeds as pepstatin A inhibited this activity in a crude seed extract. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.