Hydrogenase in Frankia KB5: Expression of and relation to nitrogenase

The localization and expression of the hydrogenase in free-living Frankia K B5 was investigated immunologically and by monitoring activity, focusing on its relationships with nitrogenase and H-2. Immunological studies revealed that the large subunit of the hydrogenase in Frankia KB5 was modified post -translationally, and transferred into the membrane after processing. The l arge subunit was constitutively expressed and no correlation was found betw een hydrogenase activity and synthesis. Although H-2 was not needed for ind uction of hydrogenase synthesis, exogenously added H-2 triggered hydrogen u ptake in medium containing nitrogen, i.e., in the hyphae. A correlation bet ween nitrogenase activity and hydrogen uptake was found in cultures grown i n media without nitrogen, but interestingly the two enzymes showed no co-re gulation.