Antioxidant properties of albumin during the oxidation of linolenic acid and low density lipoproteins in the presence of ferrous ions.

A spin-labelled fatty acid with an epr spectrum that is sensitive to the localization of the probe was used to show that albumin binds free fatty acids present in solution and also free fatty acids present in low density lipoproteins (LDL). Furthermore, albumin binds the thiobarbituric acid-reactive (TBA-reactive) products formed during the oxidation of linolenic acid, whereas the TBA-reactive substances formed during the oxidation of LDL are not bound by albumin. Linolenic acid bound to albumin essentially does not undergo peroxidation in the presence of ferrous ions, in contrast to a suspension of linolenic acid and LDL in which peroxidation occurs quite readily in the presence of ferrous ions. The highest rate of oxidation was found for linolenic acid alone. Albumin-bound spin-labelled fatty acid was essentially not reduced by ferrous ions, whereas free fatty acid or fatty acid incorporated into LDL was reduced quite rapidly, the highest rate of reduction being for free fatty acids. Thus the ability of fatty acids to undergo oxidation correlates with their accessibility to ferrous ions. The data obtained indicate that serum albumin is a relatively effective antioxidant in the blood and its mode of action is based on the immobilization of free fatty acids.