On the Physiology o/Amine Formation in the Marine Red Alga Polysiphonia urceolata
The ceramiaceaen Polysiphonia urceoIata rapidly degrades 14C(U)-L-lencine, added to sea water at a final concentration of 2.5 x 10 -5 M/l, to isoamylamine. Under experimental conditions, 22 % of the total radioactivity is found in the amine within 160min. The amino acid decarboxylase responsible for this reaction has been characterized by Hartmann (1972 a). No other mechanisms of leucine degradation could be detected, and the rate of ~4C-incorporation into algal proteins is considerably lower than that of decarboxylation. The rate of decarboxylation is optimal at a leucine concentration of about 5 x t0 -~ M/1. The amine formed is found in almost equal amounts in algal extract and environment. No further degradation of isoamylamine could be detected. The amine is a metabolic end product in P. urceolata. When ltC-isoamylamine is used as a tracer, relatively high amounts of amine are found in the algal extracts. It is supposed that the amine does not accumulate within the algal cells, but rather is bound to the acid polysaceharides of the cell walls by means of ionic exchange. The results strongly suggest tha$ decarboxylation is the main route by which P. urceolata metabolizes amino acids from ~he environment which are substrates of the decarboxylase. The endogenous amino acid pool does not seem to be available to the enzyme as a substrata source. A possible ecomgical significance of amino acid decarboxylations is discussed.