Amino acids

We propose to use on-deck/laboratory incubations to trace the fate of N in amino acids in the ocean. We will trace the fate of 9 different amino acids, including phenylalanine (Phe), glutamic acid (Glu), arginine (Arg), leucine (Leu), methionine (Met), tryptophan (Trp), aspartic acid (Asp), proline (Pro), and serine (Ser), and monitor their transformation in surface ocean. Our overarching hypothesis is that a higher percentage of N from essential amino acids will contribute to the production of refractory DON than those non-essential ones. The main approach to test the hypothesis is through our recently developed methods for 15N analysis. We will quantitatively measure each 15N form (NH4, NO2, NO3, PON, and DON) during the amino acid degradation, and identify 15N-DON molecules using advanced mass spectrometry. Through on-deck incubation of 15N-labeled amino acids, our two specific objectives are to: (1) Quantify the proportions of amino acid N that is remineralized to inorganic N, labile DON, and relatively refractory DON throughout the incubation, and (2) Characterize the amino acid-derived DON on a molecular level, which will be further used to expand the established amino acid-derived DON database, and to determine whether the amino acid derived DON is present in natural samples.