Variation of proteins, enzyme markers and gangliosides in myelin subfractions

A discontinuous sucrose gradient was used to separate adult rat brain myelin into light, medium and heavy subfractions. Basic proteins decreased sharply, proteolipid potein changed very little, and high molecular weight proteins increased from the light to the heavy fraction. The concentration of monosialoganglioside G_M1 was the highest in the middle fraction. The amount of carbohydrate in the major myelin-associated glycoprotein per mg total myelin protein increased 3.5-fold from the light to the heavy fraction. 2′,3′-Cyclic nucleotide 3′-phosphohydrolase, which is related to myelin or the oligodendroglial membrane, and acetylcholinesterase, which is in neural membranes such as the axolemma, both increased between the light and the heavy fraction, although their relative distributions among the three fractions were different. The glycoprotein and 2′,3′-cyclic nucleotide 3′-phosphohydrolase had similar distributions suggesting that they were concentrated in similar locations, possibly in the loose myelin and oligodendroglial plasma membrane. Electron microscopic examination of the subfractions was consistent with this interpretation.