26 THE DISTRIBUTION OF FORMIC AND ALCOHOL DEHYDROGENASES IN THE HIGHER PLANTS, WITH PARTICULAR REFERENCE TO THEIR VARIATION IN THE PEA PLANT DURING ITS LIFE CYCLE. By Daphne C. Davison, M.Sc. (From the Department of Biochemistry, University of Sydney.) (Nine Text-figures.) [Read 30th March, 1949.] Introduction. In the study of any enzyme it becomes necessary to obtain some idea of its distribu-tion in nature. So it was that the present investigation arose from a study of the formic dehydrogenase system of pea seeds. This dehydrogenase has only been reported in the seeds of pea and the French or Kidney bean so that the problem to be attacked was whether it occurred in other plants and if so was there any generic significance in its distribution. As a companion study the distribution of alcohol dehydrogenase has also been investigated. Thunberg (1921, 1936a) first discovered a formic dehydrogenase in the seeds of Phaseolus vulgaris (French bean). The same enzyme, obtained from peas by Fodor and Frankenthal (1930), was found to differ from the formic dehydrogenase of bacteria in that it required a coenzyme which was present in boiled pea juice and, to a lesser extent, in boiled yeast juice. Andersson (1934) and Lichtenstein (1936) were able to identify this factor as coenzyme I. In 1937 Adler and Sreenivasaya, again using peas, studied the formic dehydrogenase system in detail. They drew attention to the strong inhibition obtained with small amounts of cyanide, a property differentiating this enzyme from all hitherto known cozymase-requiring dehydrogenases. The alcohol dehydrogenase of plants is much better known than is formic dehydro-genase and although alcohol does not seem to be readily oxidized in some plants (Thomas and Fidler, 1941), the presence of an active alcohol dehydrogenase has been reported from many sources. Thunberg (1921, 1929, 19366) found the enzyme in the following species: Phaseolus vulgaris (French bean), Citrus aurantium (orange), Corchorus capsularis (jute), Cucumis sativus (cucumber), Echinocystic lobata (a climbing herb), Evonymus europaeus (spindle-tree), Mucuna utilus, Pistachia vera, Pisum sativum (green pea) and Poinciana regia. Andersson (1933) mentions this enzyme as one of a number of cozymase-requiring dehydrogenases found in cucumber seeds. Adler and Sreenivasaya (1937) studied the alcohol dehydrogenase of pea seeds and determined its pH optimum and equilibrium constant. Some later work by Berger and Avery (1943) includes a study of alcohol dehydrogenase as it occurs in the Avena coleoptile. These references are by no means exhaustive but point to the relatively widespread interest in alcohol dehydrogenase as a distinct contrast to the lack of attention to formic dehydrogenase by plant biochemists. Material. (a) Seeds. — Most of the seeds used in these studies were obtained from the National Herbarium, Sydney. Pea seeds (unless fresh peas are specified) were commercial household dried peas bought in 1 lb. packets. The dehydrogenase content was indepen-dent of the brand, several local brands being used. (&) Pea Plants. — These were grown in a normal garden plot between November and February. They were always used within two hours of gathering.