Distribution of various protein fractions in central and peripheral myelin

Abstract

Bovine white matter homogenates were separated into three fractions: a fraction extractable with water after NaCl treatment (Na), which is believed to correspond to the intermediate band of electron microscopy of myelin, and two fractions, one extractable with water after KCNS treatment (CNS) and the other not extractable (R) which are believed to belong to the dense band. About half of the 50% of the total proteins situated in the Na fraction was trypsin digestible. Also about half of the 7–10% of the total proteins found in the CNS fraction was trypsin-digestible. About 60% of the 40% of the total proteins of the R fraction were trypsin digestible. Most of the lipids, but no hexosamine, of the Na fraction were found to be bound to the trypsin-resistant proteins. In the CNS fraction most of the lipids and traces of hexosamine were bound to the trypsin-resistant proteins. In the R fraction most of the lipids and all the hexosamine appear to be bound to the trypsin-digestible proteins. Chloroform-methanol appears to extract only protein and hexosamine of the dense band (CNS+R) alongside all the loosely bound lipids. This indicates that the proteolipid of the central nervous system is derived only from the dense band of electron microscopy. The findings of the histochemical and chemical experiments are consistent with the view that most of the basic proteins and most lipophilic proteins are situated in the dense band. Peripheral nerve homogenates contain a bigger proportion of trypsin-digestible protein than cerebral white matter. In both the fractions which can be extracted from nerves after ionic treatments (the Na and the CNS fractions) 80–90% of the proteins are trypsin digestible. Most lipids appeared to be bound in almost equal amounts to the trypsin-digestible and trypsin-resistant proteins of each fraction, except for cerebrosides which in the R fraction are bound almost only to the trypsin-digestible proteins. Chloroform-methanol extracts from peripheral nerves a much smaller part of the proteins of each of the fractions than from central white matter, except for the Na fraction proteins which are not solubilized by the solvent mixture in either the central or the peripheral myelin.