No abstract

The capacity of carnosine to decrease free radical-induced damage was evaluated using the oxidation of brain homogenates, the 2,2'-azobis-2-amidino propane-induced oxidation of erythrocyte ghost membranes, the radiation induced inactivation of horseradish peroxidase and the 2,2'-azobis-2-amidino propane-induced inactivation of lysozyme. Carnosine addition up to 17 mM did not produce any significant protection in either lipid peroxidation system, as assayed by the oxygen uptake rate. Carnosine addition reduces the intensity of the visible luminescence emitted, apparently due to a dark decomposition of the luminescent intermediates. Carnosine addition protects horseradish peroxidase and lysozyme from free radical mediated inactivation. The mean carnosine concentrations required to inhibit the inactivation rates by 50% were 0.13 mM and 0.6 mM for horseradish peroxidase and lysozyme, respectively.

1. 2,2'-Azo-bis-amidinopropane (ABAP) thermal decomposition produces free radicals that initiate the lipid peroxidation of erythrocyte ghost membranes. 2. Addition of 6-n-propyl-2-thiouracil decreases the rate of the process, both by decreasing consumption of the natural antioxidants of the membranes and by direct interaction with the free radicals involved in the lipid peroxidation. 3. Peroxyl radicals produced in ABAP thermal decomposition inactivate lysozyme, horseradish peroxidase (HRP) and glucose oxidase, in that order. The number of enzyme molecules inactivated per radical introduced into the system increases with enzyme concentration. 4. Competitive studies employing mixtures of enzymes show that the order of reactivity of these enzymes towards the peroxyl radicals is the opposite to that obtained for the rate of enzyme inactivation. It is concluded that inactivation efficiency is determined mainly by the average number of free radicals that must react with an enzyme molecule to produce its inactivation, and that this number is directly related to the molecular weight of the enzyme.

No abstract

Abstract. The aerobic oxidation of saturated long chain fatty acids to the lower aldehyde and CO2 catalyzed by the α‐oxidase system of young leaves from germinating Pisum sativum results in concomitant excitation of the chloroplasts or/and fractions present in the α‐oxidase preparation. The excitation is attested to by both chlorophyll emission and Hill activity. This is the first case of photobiochemistry without light within a natural system.