Delta-Aminolevulnic Acid Dehydrase in Greening Bean Leaves

The enzyme 8-aminolevulinic acid dehydrase (E.C. 4.2.1.24) catalvzes the synthesis of porphobilinogen (PBG) from 2 molecules of 8-aniinolevulinic acid (ALA). ALA has been shown to be a precursor of both heme and chlorophyll (2,14) and ALA dehydrase has been reported from bacteria, animals and plants (3, 5, 6,11). Lascelles (6) reported that during adaptation to form bacteriochlorophvll in Rhodopseudomonas spheroides, ALA dehydrase activity increased but not as much as did ALA synthetase. During the preparation of this report the paper of Stobart and Thomas (16) was published in which ALA dehydrase activity in greening tissue cultures of Kalanchoe crenata was studied. Here we report on ALA dehydrase activity in intact etiolated bean leaves during illumination and we obtain similar results. In addition the influence of red and blue light are discussed. The experimental material was Phaseolus vulgaris cv. Resistant Asgrow Valentine (Charter Seed Company, Twin Falls, Idaho, Crop No. 1-5269). Growth and illumination conditions are reported fully elsewhere (15). Seeds were germinated in darkness and used on the seventh day. Continuous illumination (900 ft-c) was provided in a growth chamber at 260. The enzyme assay was based on the procedure of Loomis and Battaile (7). Polyclar AT -(insoluble polyvinylpyrrolidone) was a gift of General Aniline and Film Corporation, Uniion, New Jersey, and was purified by boilinig witlh 10 % HCl, washing with water, then acetone and drying in air. Before uise, it was hydrated by soaking overnight in water. Leaf pairs (20-40) were removed to a (lark cold room and ground in a mortar and pestle with 0.5 g Polyclar AT and 10 ml of a solution containing 200 mm tris HCl pH 7.2, 100 mM 2-mercaptoethanol, 100 mM MgCl2, 100 mm sodium ascorbate and 3 mM o-phenanthroline. The homogenate was transferred to a glass homogenizer for further disruption and then was strained through 8 layers of cheesecloth.