Decarboxylation of environmental L-leucine by marine red algae

The uptake and metabolism of ¹⁴C-L-leucine by Cystoclonium purpureum (Huds) Batt. (Rhodophyllidaceae) at concentrations of 0.5–50 μM were studied. Leucine was taken up from seawater at rates of 10–160 nmol·g^-1 fresh weight·h^-1. At low leucine levels ( 5 μM) the amino acid was preferably incorporated into cellular protein; amine formation was less than 5%. However at leucine concentrations of 50 μM, more than 30% of the total leucine taken up was decarboxylated to 3-methylbutylamine. This effect is expressed even more in Dumontia increassata (O. F. Müll) Lamour. (Dumontiaceae). In both species some of the amine occurred as a non-volatile derivative (bound amine) from which free amine could quantitatively be released by acid hydrolysis. Leucine and amine uptake were inhibited by CCCP. However, from cells preloaded with both leucine and amine, only free amine is released in the presence of CCCP. The results indicate that decarboxylase activity will be switched on at increased levels of amino acids in seawater which may be expected frequently in habitats of littoral algae (tidal zone). A possible function of amine formation and release within the scope of chemical defence of benthic algae is discussed.