A chloroplast protease capable of processing the precursor of ribulose bisphosphate carboxylase small subunit to the mature size has been purified 350-fold from stromal extracts of pea leaves. The enzyme has a molecular weight of about 180,000 daltons, a pH optimum near 9.0, and is inhibited by metal-chelators but not by serine- or thiol-protease inhibitors. The partially purified enzyme is also capable of processing the precursors of wheat and barley pre-plastocyanin to the mature size, and is therefore neither precursor- nor species-specific. The enzyme displays a high degree of reaction specificity in that it has failed to cleave all protein substrates tested other than precursors destined for the chloroplast. The small subunit precursor (molecular weight 20,000) is processed to the mature size (molecular weight 14,000) via an intermediate of molecular weight 18,000. The second cleavage can be inhibited by pre- incubation of the precursor with iodoacetate. A preliminary investigation into the basis for the specificity of the small subunit precursor processing reaction has been carried out. Proline, lysine and arginine residues in the small subunit precursor polypeptide chain have been replaced by amino acid analogues of these residues. The abnormal precursors are very poor substrates for the purified processing enzyme, and are imported into intact isolated chloroplasts at much-reduced rates. The significance of these observations is discussed with reference to the primary structure of the small subunit precursor.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:349457 |
| Date | January 1984 |
| Creators | Robinson, Colin |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/111978/ |
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