Identification of Potent Bactericidal Compounds Produced by Escapin, an l -Amino Acid Oxidase in the Ink of the Sea Hare Aplysia californica

Authors:
Publisher website
Google Scholar
Abstract
The ink of sea hares ( Aplysia californica ) contains escapin, an l -amino acid oxidase that metabolizes l -lysine, thereby producing a mixture that kills microbes and deters attacking predators. This secretion contains H 2 O 2 , ammonia, and an equilibrium mixture of “escapin intermediate product” (EIP-K) that includes α-keto-ε-aminocaproic acid and several other molecules. Components of the equilibrium mixture react nonenzymatically with H 2 O 2 to form “escapin end product” (EEP-K), which contains δ-aminovaleric acid and δ-valerolactam. The proportions of the molecules in this equilibrium mixture change with pH, and this is biologically important because the secretion is pH 5 when released but becomes pH 8 when fully diluted in seawater. The goal of the current study was to identify which molecules in this equilibrium mixture are bactericidal. We show that a mixture of H 2 O 2 and EIP-K, but not EEP-K, at low mM concentrations is synergistically responsible for most of the bactericidal activity of the secretion against Escherichia coli , Vibrio harveyi , Staphylococcus aureus , and Pseudomonas aeruginosa . Low pH enhances the bactericidal effect, and this does not result from stress associated with low pH itself. Sequential exposure to low mM concentrations of EIP-K and H 2 O 2 , in either order, does not kill E. coli . Reaction products formed when l -arginine is substituted for l -lysine have almost no bactericidal activity. Our results favor the idea that the bactericidal activity is due to unstable intermediates of the reaction of α-keto-ε-aminocaproic acid with H 2 O 2 .

This publication has 21 references indexed in Scilit: