title: Studies on subcellular fractions which are involved in myelin assembly: labeling of myelin proteins by a double radioisotope approach indicates developmental relationships.
abstract: The question of developmental relationships amongst myelin-related membranes in subfractions of myelinating mouse brain (15 days) was investigated by a time-staggered double isotope protocol using [3H]leucine and [14C]leucine. Preliminary results are interpreted and discussed in the context of a mathematical conceptualization of pulse-labeling kinetic analyses of myelin proteins in subcellular membrane compartments. Differences in ratio of the two leucine labels among proteins of myelin-containing subfractions are interpreted as confirming metabolic differences relating to various stages of development rather than precursor-product relationships. The incorporation into myelin of 14K, 17K, and 18.5K basic proteins (MBPs) occurs with relatively short delay times, following their synthesis (less than 5 min), and seems to occur simultaneously into all compartments. The 21.5K MBP and the proteolipid protein, on the other hand, require 10-14 min and 14-20 min, respectively. A scheme is presented to illustrate the probable assignment of subfractions to various myelin "compartments" during myelination, and to serve as a working hypothesis for studies on precursor-product relationships.
mesh_terms: D000818:Animals; D001921:Brain / Q000254:growth & development* / Q000648:ultrastructure; D002250:Carbon Radioisotopes; D007553:Isotope Labeling / Q000379:methods*; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D051379:Mice; D004676:Myelin Basic Protein / Q000378:metabolism; D009185:Myelin Proteins / Q000378:metabolism*; D009186:Myelin Sheath / Q000502:physiology* / Q000648:ultrastructure; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D004676:Myelin Basic Protein; D009185:Myelin Proteins; D014316:Tritium; D007930:Leucine