UPTAKE OF AMINO ACIDS BY PAREURYTHOE CALIFORNICA: SUBSTRATE INTERACTION MODIFIES NET INFLUX FROM THE ENVIRONMENT

Pareurythoe californica is capable of simultaneous net uptake of 18 amino acids, each present at an initial concentration of 200 nM. Rates of uptake are comparable for all amino acids tested. Kinetics of uptake are well described by the Michaelis-Menten equation. Neither bacteria nor other epifauna play a significant role in the observed uptake. The net entry of the amino acids tested was inhibited in the presence of equimolar concentrations of representatives of all major classes of amino acids (i.e., polar and nonpolar neutral, dicarboxylic, polybasic) at concentrations comparable to those found in the environment. Thus, a mixture mimicking the composition and concentration of substrates normally present in the environment was used to obtain a more realistic estimate of entry rates under natural conditions. When this was done, the contribution of exogenous amino acids to the nitrogen needs (based on ammonia excretion) and the requirement for reduced carbon (based on oxygen consumption) of Pareurythoe ranged from 10% to 50%, depending on levels of substrate available in the environment.