Interactions of H and carbon metabolism in moderating nitrogenase activity of the Gunnera/Nostoc symbiosis.

Nitrogenase activity in the Gunnera Nostoc symbiosis is shown to respond dramatically to the addition of glucose. H can replace glucose in stimulating nitrogenase activity, but there is no H stimulation in the presence of excess glucose. Net hydrogen evolution is strongly stimulated by addition of glucose. We postulate that carbohydrate supply and uptake hydrogenase can moderate the apparent activity of nitrogenase by supplying reductant and/or ATP. The recycling of a large proportion of the electron flux in nitrogenase through uptake hydrogenase maintains a high level of potential nitrogenase ready to take advantage of an influx of carbohydrate. [ABSTRACT FROM AUTHOR]