Proteolipides, a new type of tissue lipoproteins; their isolation from brain.

Brain tissue and brain tumor tissue have been found to contain a new type of component to which the name of proteolipides has been given (1). Proteolipides are lipoproteins having as constituents a lipide moiety and a protein moiety, but, while other known lipoproteins are soluble in water or salt solutions, proteolipides are insoluble in water and soluble in chloroform-methanol mixtures; i.e., their solubilities are akin to those of lipides. It is to emphasize this special feature that the name proteolipides has been coined. Proteolipides are found in all tissues that have been studied, with the exception of blood plasma. The tissue that is richest in them is white matter of brain in which proteolipide protein constitutes 2.0 to 2.5 per cent of the weight of wet tissue. Gray matter is the second richest tissue in them, closely followed by heart muscle. Kidney, liver, lung, skeletal muscle, and smooth muscle contain proteolipides in smaller amounts than do heart muscle or than brain. Brain tumors range between white matter and gray matter in proteolipide content. Most of the work reported here has been carried out on white matter. From it have been isolated three different proteolipide fractions, one of which was obtained consistently as a crystalline substance. The first indication of the existence of proteolipides was the observation that lipide extracts prepared from brain tissue, by a method described in an accompanying paper (Z), and presumably free of non-lipide contaminants, contained more N than could be expected from their phosphatide and cerebroside content. In an attempt to isolate the lipide fraction which contained this unidentified lipide N, it was found that, on drying