Biosynthesis and function of trehalose inEctothiorhodospira 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, haloalkaliphilic bacteriumEctothiorhodospira halochloris. The activity is stabilized by 20mM MgCl₂, 50mM 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°C. The K_m-values were 1.5×10^–3M for UDP-glucose and 2×10^–3M 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.