Specific antibodies have been developed against PI, P2, and Po myelin proteins and were used to study the localization of these proteins in the rat peripheral nervous system. Both peripheral and central nervous system myelin sheaths contain Pi protein. Po and P2 proteins are found exclusively in peripheral nervous system myelin sheaths. Antisera to Pi and Po proteins stain all peripheral nervous system myelin sheaths uniformly. P2 protein is not a component of all peripheral nervous system myelin sheaths. In sheaths that do contain P2 protein, it is concentrated in the area of the Schmidt-Lanterman incisures.Myelin isolated from mammalian peripheral nervous system (PNS) contains three major proteins (1). These proteins include a glycoprotein, Po, with a molecular weight (Mr) of 30,000 and two basic proteins, PI and P2, with Mr of 18,500 and 13,500, respectively. The Po and P2 proteins are unique to PNS myelin whereas the P1 protein appears to be identical to the large central nervous system (CNS) myelin basic protein (2). The Po protein represents approximately 50% of total PNS myelin protein whereas the quantities of PI and P2 and the ratio of P1/P2 varies from species to species (1). The ratio of PI/P2 also varies within different PNS fiber tracts obtained from the same animals (1). Myelin purification provides a heterogeneous population of myelin membranes. By virtue of the myelin isolation procedure, anatomical specificity of myelin proteins within individual myelinated fibers or myelin internodes is lost prior to biochemical analysis. Indirect evidence has localized the Po protein at the intraperiod line (3-5) and the basic proteins at the major dense line (5-7) of myelin. These studies have not defined the anatomical distribution of the major PNS myelin proteins within myelin sheaths of PNS fiber tracts.In the present study we present light microscopic immunocytochemical evidence that in the rat P2 protein is not a component of all PNS-myelin sheaths, but in fact is a component of only some myelin sheaths. In addition, when antiserum to P2 stains a myelin sheath, Schmidt-Lanterman clefts stain more intensely than compact portions of the internode. Po and PI proteins are located in all PNS myelin sheaths thus far analyzed, and antisera to them stain all sheaths uniformly. MATERIALS AND METHODSSeven-day-old, 25-day-old, and adult (200-225 g) SpragueDawley rats were anesthetized with ether and fixed by intracardiac perfusion with a solution containing 76 ml of saturated HgCl2 and 20 ml of 37% (vol/vol) formaldehyde. Trigeminal

No abstract

No abstract

Concanavalin A strongly agglutinates purified fragments of immature and mature rat brain myelin, but only weakly agglutinates mature bovine and human myelin fragments. A sensitive method involving [3H]concanavalin binding to sodium dodecyl sulphate/polyacrylamide gels was used to detect the concanavalin A-binding proteins in purified myelin. When applied to mature rat brain myelin proteins that had been labelled in vivo with [14C]fucose, the distribution of the [3H]concanavalin A on the gel was very similar to that of [14C]fucose with the major peak corresponding to the major myelin-associated glycoprotein. The technique revealed that the immature form of the myelin-associated glycoprotein with a slightly larger apparent molecular weight also bound concanavalin A, and that in purified immature rat myelin the quantitative importance of some of the other glycoproteins in binding concanavalin A was increased relative to the myelin-associated glycoprotein. The separated proteins of bovine and human myelin bound more [3H]-concanavalin A than those of rat myelin. In these species, the myelin-associated glycoprotein was a major concanavalin A-binding protein, although two higher-molecular-weight glycoproteins also bound significant quantities of [3H]concanavalin A. The results indicate that there are receptors for concanavalin A on the surface of rat, bovine and human myelin membranes and suggest that the myelin-associated glycoprotein is one of the principal receptors.

Myelin isolated from the central nervous system of Xenopus tadpoles was characterized biochemically and compared with Xenopus frog and mammalian myelins. Xcnopi4.s tadpole myelin contains the characteristic protein and lipid components of mammalian myelin, although quantitative differences exist. The biochemical composition of Xenopirs tadpole myelin suggests that it is an immature form of XPnopus frog myelin. Basic protein and proteolipid protein are prominent components of Xenopus myelin, but isolated tadpole myelin contains a greater proportion of higher molecular weight proteins than Xenopirs frog or mature mammalian myelin. The basic protein has a higher apparent molecular weight than mammalian myelin basic protein. The levels of 2',3'-cyclic nucleotide 3'-phosphodiesterase are significantly higher in whole tadpole brain homogenate and purified myelin than in similar mammalian preparations. Tadpole myelin lipids contain a higher proportion of phospholipids and less galactolipid than mammalian myelin. Tadpole myelin galactolipids include a high (16%) percentage of monogalactosyl diglyceride, a component found in only trace quantities (0.9%) in bovine myelin.