Sulfate activation in Rhodobacter sulfidophilus and other species of the Rhodospirillaceae

Rhodobacter sulfidophilus, R. capsulatus, R. sphaeroides, Rhodospirillum rubrum, Rhodopseudomonas palustris, R. viridis and Rhodocyclus gelatinosus were found to be able to synthesize adenylylsulfate and 3-phosphoadenylylsulfate from sulfate and ATP. The presence of ATP sulfurylase was proven for the soluble protein fractions of all these species. ADP sulfurylase was not found. ATP sulfurylase was purified from R. sulfidophilus. Its molecular weight was 290,000. The enzyme is stabilized by magnesium ions and elevated salinities. The optimal pH was 8.0, activity was found between pH 6.8 and 9.4. The enzyme is inactivated at temperatures above 40°C. Kinetic studies resulted in K_m(ATP)=0.26 mM, K_m(sulfate)=0.33 mM; K_i(AMP)-2.1 mM, K_i(ADP)=1.15 mM; K_i(APS)=0.8 M; K_i(sulfite)=0.4. mM; K_i(sulfide)=0.66mM.Uncommon abbreviations APS adenylylsulfate - PAPS 3-phosphoadenylylsulfate - PEP phosphoenolpyruvateDedicated to Professor Gerhart Drews on the occasion of his 60th birthday