MOLYBDENUM AND VANADIUM DO NOT REPLACE TUNGSTEN IN THE CATALYTICALLY ACTIVE FORMS OF THE 3 TUNGSTOENZYMES IN THE HYPERTHERMOPHILIC ARCHAEONPYROCOCCUS-FURIOSUS

Three different types of tungsten containing enzyme have been previous ly purified from Pyrococcus furiosus (optimum growth temperature, 100 degrees C): aldehyde ferredoxin oxidoreductase (AOR), formaldehyde fer redoxin oxidoreductase (FOR), and glyceraldehyde-3-phosphate oxidoredu ctase (GAPOR). In this study, the organism was grown in media containi ng added molybdenum (but not tungsten or vanadium) or added vanadium ( but not molybdenum or tungsten). In both cell types, there were no dra matic changes compared with cells grown with tungsten, in the specific activities of hydrogenase, ferredoxin:NADP oxidoreductase, or the 2 k eto acid ferredoxin oxidoreductases specific for pyruvate, indolepyruv ate, 2-ketoglutarate, and 2-ketoisovalerate. Compared with tungsten-gr own cells, the specific activities of AOR, FOR, and GAPOR were 40, 74, and 1%, respectively, in molybdenum-grown cells, and 7, 0, and 0%, re spectively, in vanadium-grown cells. AOR purified from vanadium-grown cells lacked detectable vanadium, and its tungsten content and specifi c activity were both ca. 10% of the values for AOR purified from tungs ten-grown cells. AOR and FOR purified from molybdenum-grown cells cont ained no detectable molybdenum, and their tungsten contents and specif ic activities were >70% of the values for the enzymes purified from tu ngsten-grown cells. These results indicate that P. furiosus uses exclu sively tungsten to synthesize the catalytically active forms of AOR, F OR, and GAPOR, and active molybdenum- or vanadium-containing isoenzyme s are not expressed when the cells are grown in the presence of these other metals.