CELL-SURFACE OXIDATION OF AMINO-ACIDS IN SEAWATER

Recently, it was shown that certain phytoplankton species in laborator y culture can use cell-surface enzymes to oxidize amino acids and amin es and take up ammonium produced during the oxidation. Previously, we developed a fluorescent analog of the amino acid lysine (LYA-lysine) t o act as a tracer of cell-surface oxidation processes. In the present study, a kinetic approach demonstrated that these fluorescent probes e ffectively compete with natural amino acids and are thus similar to th e natural compounds. Field studies showed that naturally occurring phy toplankton and bacteria-size organisms oxidized the fluorescent analog , extending the discovery of this oxidation process to natural waters. Parallel experiments measuring uptake of C-14-labeled amino acids and oxidation of LYA-lysine showed that oxidation rates could be as much as 40% of the total removal rate. This finding suggests that removal o f amino acids from seawater might be significantly underestimated if u ptake across the cell membrane were the only process considered. Howev er, cell-surface oxidative deamination was detected only in summer, wh en temperatures exceeded 22 degrees C.