STUDIES OF THE MECHANISM OF DEMYELINATION REGIONAL DIFFERENCES IN MYELIN STABILITY IN VITRO

Studies on the Wolfgram high molecular weight CNS myelin proteins: relationship to 2',3'-cyclic nucleotide 3'-phosphodiesterase

Evidence is presented that the major protein components of the high molecular weight CNS myelin proteins designated as the Wolfgram protein doublet (W1 and W2) contain the enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37, CNP). CNP is a basic hydrophobic protein containing about 830 to 840 amino acid residues. When electrophoresed on SDS polyacrylamide gels, CNP appears as a protein doublet, separated by a molecular weight difference of about 2500-3000 in bovine, human, rat, guinea pig, and rabbit. A similar protein doublet has been identified as the Wolfgram proteins W2 and W1 in myelin and in the chloroform-methanol-insoluble pellet obtained from myelin. Moreover, the relative Coomassie blue staining intensity of the CNP2 plus CNP1 protein doublet among the species examined was remarkably similar to that observed for electrophoresed myelin and chloroform-methanol-insoluble pellet derived from myelin. Antisera raised against purified bovine CNP recognized the W1 and W2 proteins isolated from bovine and human brain. The amino acid composition of pure bovine CNP is presented and compared with the compositions of several rat and bovine Wolfgram proteins obtained by other investigators. Our electrophoretic, compositional, and immunological data support the contention that the enzyme CNP is a major component of the Wolfgram protein doublet.

An X-ray diffraction comparison of myelins from the human nervous system

Earlier small-angle X-ray diffraction studies have indicated that central and peripheral nerve myelins may be significantly different structurally, although relatively few examples for each system and for individual species have been examined. In order to understand better the intra- and inter-system relationships, this study has developed more extensive information for a single species: six cases centrally and ten peripherally, featuring cranial nerves and a few others of the human nervous system. Peripheral myelin spacings (membrane pair thicknesses) are relatively similar, 184.4 +/- 1.40 A, and the ratios of diffraction peak height intensities of the second to fourth orders are also closely bunched: 1.85 +/- 0.216. Central myelin spacings and intensity ratios are distinctly different and more variable: spacings 160.3-165.8 A and intensity ratios 2.81-4.46. It appears that within a given species or between closely related (e.g., mammalian) species peripheral myelins possess relatively invariant structures, though significant spacing declines are encountered for both systems as phylogenetic relationships become more distant. The observed greater variability of CNS structures within a single species may correspond to known compositional differences between CNS regions or result from observational difficulties. In any case there is a marked discontinuity between the myelin structures of CNS and PNS nerves.

A lymph node neutral proteinase acting on myelin basic protein

A neutral protease present in inguinal and popliteal lymph nodes of rats with acute experimental allergic encephalomyelitis (EAE), rats injected with Freund's adjuvant, and rats that are normal has been found to hydrolyze basic protein present in purified brain and spinal cord myelin. The enzyme has been enriched by ammonium sulfate precipitation, and its properties have been studied. The protease activity toward different substrates was very specific and decreased in the following order: Protamine sulfate = polylysine (MW 183,000) > myelin basic protein > histone > polylysine (MW 2000) > polyarginine > cytochrome c. Other proteins including casein, freshly denatured hemoglobin, egg albumin, bovine serum albumin, and ribonuclease were ineffective as substrates. The pH curve showed a peak at pH7 for rat myelin, isolated beef basic protein, and histone. A possible role for this enzyme in demyelination in acute experimental allergic encephalomyelitis is suggested.