Singlet oxygen reaction of mycosporine glycine as a suppressor of photosensitization in marine organisms

Abstract

This report concerns physiological function of mycosporine-like amino acids (MAA) as an active defense against photooxidative sunlight effects in marine organisms. In biological model systems, mycosporine glycine (MG) that is a representative member of MAA family was found to efficiently suppress singlet oxygen (1O2)-mediated photodynamic effects, such as hemolysis of erythrocytes, inhibition of mitochondrial respiratory activity and inactivation of lactate dehydrogenase. The relative singlet oxygen (1O2) quenching efficiency was assessed by ESR experiment with a 1O2 trap compound 2,2,6,6-tetramethyl-4-piperidone. Since MG turned out to be more effective than a well known scavenger histidine, the rate constant of its reaction with 1O2 was measured by both steady state method and time resolved method, the former being based on inhibition of the selfsensitized photooxidation of rubrene and the latter on increase in the decay rate constant of 1O2 measured from time-resolved decay signal of 1O2 phosphorescence by the added MG. The rate constant of MG-1O2 reaction was determined to be 6.5 x 107 M-1s-1 by the rubrene method and 5.6 x 107 M-1s-1 by the time-resolved method. The results suggest that MG probably together with some other active MAA may play an important role in protecting marine organisms against sunlight-damage by eliminating 1O2 generated from certain endogenous photosensitizers.