title: Are prosome particles formed by the disintegration of proteasomes?
abstract: Quail reticulocyte 19S "prosome" fractions isolated on sucrose density gradients contain two kinds of particles: cylindrical proteasomes and ferritin. When samples of this fraction are prepared for electron microscopy using the one-step stain protocol described in this paper, most of the particles have a rectangular image resembling the proteasome. However, when samples are prepared for electron microscopy using the two-step stain protocol described here, there are few rectangular images. Their place is taken by round particles that resemble the prosome. Thus it appears that the round, raspberry-shaped particles called prosomes and the ring-like proteasome particles may be artifacts of specimen preparation for electron microscopy. We propose that proteasome particles may disintegrate when prepared for electron microscopy by methods such as the two-step stain protocol and that prosome particles represent the component parts of the proteasome. Furthermore, based on the enhancement of proteasome images obtained using the one-step main protocol we propose that, instead of consisting of a stack of four rings, the proteasome is constructed of three components, i.e., a spherical central particle flanked by two flat hexagonal end caps.
authors.affiliation: Department of Zoology, University of Western Ontario, London, Canada.
authors.forename: T W
authors.initials: TW
authors.lastname: Blaker
authors.forename: M
authors.initials: M
authors.lastname: Locke
authors.forename: B G
authors.initials: BG
authors.lastname: Atkinson
mesh_terms: D000818:Animals; D016477:Artifacts; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000302:isolation & purification / Q000648:ultrastructure*; D019286:Endopeptidase K; D005293:Ferritins / Q000032:analysis / Q000648:ultrastructure; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D009097:Multienzyme Complexes / Q000187:drug effects / Q000302:isolation & purification / Q000648:ultrastructure*; D016624:Negative Staining; D046988:Proteasome Endopeptidase Complex; D011784:Quail; D012156:Reticulocytes / Q000201:enzymology*; D012697:Serine Endopeptidases / Q000494:pharmacology
chemical_list: D009097:Multienzyme Complexes; D005293:Ferritins; D012697:Serine Endopeptidases; D019286:Endopeptidase K; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex