Comparison of cell-surface L-amino acid oxidases from several marine phytoplankton

Abstract

Phytoplankton possess cell-surface oxidases that oxidize amino acids and primary amines to produce extracellular H 2 0 2 , NH4+, and a-keto acids (from amino acids) or aldehydes (from primary amines). The NH,+ is subsequently taken up and used for growth. A survey of marine phytoplankton shows that at least 3 genera possess cell-surface L-amino acid oxidases: Pleurochrysis and Pryrnnesium (prymnesiophytes), and Arnphidinium (a dinoflagellate). These enzymes are quite similar, with halfsaturation concentrations of ca 0.1 to 0.5 PM, but differ in their inhibition by the nonspecific protease proteinase K, and a detergent, lithium dodecyl sulfate.

Differential coral bleaching—Contrasting the activity and response of enzymatic antioxidants in symbiotic partners under thermal stress

“…Potential leakage of hydrogen peroxide from Symbiodinium and other dinoflagellates (but also extracellular generation of ROS) has indeed been shown experimentally (Palenik and Morel, 1990;Sandeman, 2006;Suggett et al, 2008;Saragosti et al, 2010). Our findings agree with previous studies that, depending on the coral species, catalase activity per unit protein is usually three to ten times higher (up to twenty-three times in M. digitata) in the host than in the symbiont (Yakovleva et al, 2004;Levy et al, 2006;Higuchi et al, 2008).…”

Cell-surface proteolytic activity of photosynthetic dinoflagellates

“…Amino acid oxidases on the surface of phytoplankters can degrade amino acids, releasing ammonium, which is readily assimilated (Palenik & Morel 1990a). Amino acid oxidases have been found in dinoflagellates (Palenik & Morel 1990b). By releasing amino acids at the cell surface, ecto-proteolytic enzymes, such as LAP, might facilitate uptake of nitrogen by providing substrate for amino acid oxidases.…”

Cycling of biologically available nitrogen in riverine humic substances between marine bacteria, a heterotrophic nanoflagellate and a photosynthetic dinoflagellate

“…This was perhaps due to the utilization of different DON compounds by the phytoplankton community in the stratified water mass they investigated. Several phytoplankton species are able to use N bound in different LMW organic compounds such as urea and free and combined dissolved amino acids (see reviews by Flynn & Butler 1986, Antia et al 1991, and some phytoplankton species have cell-surface amino acid oxidases which oxidize amino acids and primary amines to ammonium for cellular uptake (Palenik & More1 1990). HMW polymeric compounds such as HS are too large to pass the cytoplasmic membrane (Payne 1980) and must be degraded enzymatically before uptake (Raven 1980), or taken up actively via pinocytosis, a mechanism in which the plasma membrane extends and forms a vesicle enclosing liquid containing the HMW compounds (Klut et al 1987); this mechanism has so far been very little studied and the importance of it for phytoplankton nutrition is virtually unknown.…”