The analytical approach to the nature of lipofuscin (age pigment).

Analytical studies of three lipopigments show that much can be achieved. Lipopigment from ovine ceroid-lipofuscinosis is composed of discrete protein and lipid molecules in orderly arrays and lipid peroxidation is not involved in its formation. Subunit c of mitochondrial ATP synthase accounts for approximately 50% of accumulated material and is specific to the disease process in this and other forms of the disease. Lipofuscin from bovine heart was mostly soluble and also contained discrete proteins, lipids and metals. Equine thyroid lipofuscin was less soluble but also had a relatively high protein content, probably derived from thyroglobulin. Although sugar could not be measured quantitatively, staining reactions and elemental analyses suggested it could also be a significant component. Some may be present as derivatives in the form of advanced glycation products. It is proposed that protein, the dominant molecular species present, is the important constituent in lipofuscinogenesis rather than lipid peroxidation. Whereas this latter may play some part in the maturation of lipofuscin, this has not been shown experimentally and is not likely to be the initiating mechanism.