title: The cellular origin of glyoxysomal proteins in germinating castor-bean endosperm.
abstract: The capacity of castor-bean endosperm tissue to incorporate [35S]methionine into proteins of the total particulate fraction increased during the first 3 days of germination and subsequently declined. At the onset of germination 66% of the incorporated 35S was found in the separated endoplasmic-reticulum fraction, with the remainder in mitochondria, whereas at later developmental stages an increasing proportion of 35S was recovered in glyoxysomes. The kinetics of [35S]methionine incorporation into the major organelle fractions of 3-day-old endosperm tissue showed that the endoplasmic reticulum was immediately labelled, whereas a lag period preceded the labelling of mitochondria and glyoxysomes. When kinetic experiments were interrupted by the addition of an excess of unlabelled methionine, incorporation of [35S]methionine into the endoplasmic reticulum rapidly ceased, but incorporation into mitochondia and glyoxysomes continued for a further 1h. Examination of isolated organelle membranes during this period showed that the addition of unlabelled methionine resulted in a stimulated incorporation of [35S]no methionine into the endoplasmic-reticulum membrane for 30 min, after which time the 35S content of this fraction declined, whereas that of the glyoxysomal membranes continued to increase slowly. The 35S-labelling kinetics of organelles and fractions derived therefrom are discussed in relation to the role of the endoplasmic reticulum in protein synthesis during glyoxysome biogenesis.
mesh_terms: D002367:Ricinus communis / Q000254:growth & development* / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D008830:Microbodies / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D009940:Organoids / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D010947:Plants, Toxic; D012278:Ricinus / Q000254:growth & development*
chemical_list: D010940:Plant Proteins; D008715:Methionine