Dry pea seed proteasome : purification and enzymic activities.

Proteasomes were isolated from mature, dry pea seeds (Pisum sativum L.). They appear to be similar to proteasomes from other sources in that they are cylindrical (shown by negative staining), have a molecular mass greater than 600 kilodaltons (by gel permeation chromatography), and consist of several subunits between 25 and 31 kilodaltons. The seed proteasomes possess three characteristic partial activities (trypsin-like, chymotrypsin-like, and peptidyl glutamyl peptidase) as determined with fluorogenic peptide substrates. Activation and inhibition by various effectors, and particularly sensitivity to porphyrins, also match characteristics of proteasomes described for other organisms. The potential role of the proteasome in seed biology is discussed.