Biosynthesis and function of trehalose in Ectothiorhodospira halochloris.

Trehalose 6-phosphate synthase, catalyzing the reaction between UDP-glucose and glucose 6-phosphate and forming trehalose 6-phosphate, was isolated and partially purified (30-fold) from the phototrophic, halo-alkaliphilic bacterium Ectothiorhodospira halochloris. The activity is stabilized by 20 mM MgCl2, 50 mM NaCe and 2M glycine betaine. The molecular weight was 63000. The enriched enzyme had a MgCl2 optimum at 3-6mM, a pH optimum at 7.5 (in Tris-HCl buffer) and a temperature optimum at 50 degrees C. The Km-values were 1.5 x 10(-3) M for UDP-glucose and 2 x 10(-3) M for glucose 6-phosphate. The enzyme showed a salinity dependence with optimal concentrations between 100 and 300mM salt. Higher concentrations of salt resulted in a decrease in activity. In the presence of inhibitory salt concentrations the compatible solute glycine betaine had a protective effect with a maximum between 0.5 and 2.0M.