Protein-lipid combinations abundant in brain tissue, but also present in a wide variety of animal and plant tissues. In contrast to lipoproteins, they are insoluble in water, but soluble in a chloroform-methanol mixture. The protein moiety has a high content of hydrophobic amino acids. The associated lipids consist of a mixture of glycerophosphates; cerebrosides; and sulfoglycosphingolipids; while lipoproteins contain phospholipids; cholesterol; and triglycerides.