Biogeochemistry of mycosporine-like amino acids (MAAs): A new perspective on UV-absorbing compounds via liquid chromatography-mass spectrometry.

摘要

Increasing ultraviolet (UV) radiation as a result of the seasonally re-occurring ozone hole over Antarctica has stimulated interest in UV-photoprotective mechanisms utilized by marine organisms. The deleterious effects of UV radiation on marine organisms coupled with the interaction of UV and dissolved seawater components presents a cause for concern at an ecological scale. Mycosporine-like amino acids (MAAs) are a class of secondary metabolites absorbing strongly in the UV region (300–360 nm). MAAs are produced by phytoplankton, algae and cyanobacteria from geographically diverse environments, including Antarctica. My goal was to find a sensitive method to detect and characterize MAAs and to use this method to understand the mechanisms by which they are produced and released by an Antarctic phytoplankter, examine their trophic transfer and dietary alteration and to study their photoreactivity in the dissolved state.; Due to a lack of commercial standards, a mass spectral (MS) approach was taken to identify individual MAAs. A matrix of chromatographic retention time, wavelength maximum and molecular weight allows the determination and identification of commonly occurring MAAs. A descriptive analysis LC-MS-MS and gas chromatographic-MS fragmentation patterns was compiled for several MAAs and will assist in categorizing hereto-unidentified MAAs. This analytical approach allowed the examination and initial characterization of UV-absorbing compounds in Phaeocystis antartica, an important member of the Antarctic phytoplankton community. The sunscreen protection afforded by MAAs is not limited to primary producers such as P. antarctica but is also trophically transferred to grazers and primary carnivores. MAAs are also released and incorporated into the dissolved organic matter pool. Photodegradation studies with MAAs revealed that they are highly photostabile requiring a photosensitizing agent for appreciable photodegradation. Over all, evidence continues to build for the role of MAAs as UV sunscreens. Their importance is highlighted by their presence at various trophic levels and their photostability in aqueous mediums gives credit to their efficiency as sunscreens. Using the mass spectral tools developed during these studies, we can now begin to understand their ecological function and as well as their potential environmental fates at a structural and mechanistic level that had not been previously possible.