Nitrogenase--hydrogenase interrelationships in Rhizobia.

A review is given of the properties of the hydrogenase present in Rhizobium bacteriods together with a discussion and evidence of the function of the enzyme in relationship to nitrogen fixation. The efficiency with which nodules fix nitrogen i.e. the amount of hydrogen evolved as a ratio of the total electron flow through nitrogenase, is considered and the recycling of hydrogen is discussed. Attention is drawn to recent work, in which plants which have nodules containing hydrogenase have been shown to fix more nitrogen and increase more in dry matter than plants with nodules without hydrogenase.

Choline acetyltransferase in the nettle Urtica dioica L.

Extracts of acetone-dried powders prepared from nettle leaves were shown to catalyse the synthesis of acetylcholine. The specific activity of the enzyme in these extracts is of the same order as that of extracts from mammalian sources, such as ox brain, and the effects of temperature and pH are similar to those reported for mammalian choline acetyltransferase. Synthesis is not restricted to the younger leaves but appears to be continuous up to senescence.