Dimethylsulfoniopropionate lyase from the marine macroalga Ulva curvata: purification and characterization of the enzyme

Abstract

This is a report on the purification and characterization of an algal dimethylsulfoniopropionate (DMSP) lyase. This enzyme, also found in bacteria, is responsible for producing most of the dimethylsulfide (DMS) in marine environments. It was purified from the green macroalga, Ulva curvata (Kutzing) De Toni. Initial in-vivo experiments showed that DMSP lyase activity from endogenous DMSP in Ulva increased for 24 h and then decreased as the culture aged and endogenous DMSP levels were depleted. When amended with exogenous DMSP, rates of DMSP lyase activity remained high even when the culture was 5 d old. Following disruption of the DMSP-depleted U. curvata cells by grinding, a soluble DMSP lyase was purified. This enzyme is a monomer of 78 kDa which has a Km for DMSP of 0.52 mM. Soluble DMSP lyase had an optimum pH of 8 and an optimum osmotic strength of 75 mM NaCl. Following disruption of the algae by either grinding with sand or blending, and washing out the soluble enzyme, the green tissue, when treated with the non-ionic detergent, Triton X-100, solubilized additional DMSP lyase activity. Three hydrophobic variant forms of Ulva DMSP lyase were isolated and partially characterized from the detergent-solubilized activity. While the molecular and kinetic properties of the algal enzyme are different from the bacterial enzymes we purified earlier, both the soluble and membrane-bound forms did, nevertheless, cross-react with antibodies raised against the bacterial (Alcaligenes strain M3A) DMSP lyase.