The Membrane Bound Forms of Penicillinase in Bacillus Licheniformis and Their Significance for the Secretion Process
Earlier in this conference, Dr. Palade and Drs. Blobel and Sabatini summarized the major features of the process by which mammalian cells secrete proteins (1, 2, 3, 4). (Biologically-active proteins such as enzymes, hormones or immunoglobulins are generally chosen as test systems.) There is strong evidence that the polypeptide chain is synthesized on the polysomes of the rough endoplasmic reticulum, enters the membrane in an open or incompletely-folded conformation, and is eventually found in the lumen of the rough endoplasmic reticulum. At this point the protein is already extracytoplasmic. In the large mammalian cells this polypeptide must be transported toward the exterior via the smooth endoplasmic reticulum, usually through a Golgi apparatus, and ultimately in vesicles which fuse with the plasma membrane and release their contents. During this process the protein is usually glycosylated, and there may be modification of the peptide chain itself. A similar process appears to take place in yeasts and other fungi (5, 6), although there is no direct proof that the secreted protein is produced by the polysomes of a rough endoplasmic reticulum.
KeywordsPolypeptide Chain Rough Endoplasmic Reticulum Apparent Molecular Weight Bacillus LICHENIFORMIS Smooth Endoplasmic Reticulum
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