1. Strains of Erwinia carotovora and Erwinia aroideae, formerly thought only to be inducible, are constitutive for polygalacturonic acid trans-eliminase. Maximum enzyme formation, however, occurs in the presence of polygalacturonic acid.2 . A release from strong catabolic repression enables glucose-grown cultures to initiate their attack on polygalacturonic acid and, thereby, eliminates the necessity for the entry of the polymer into the cell.3. A low constant proportion (less than 25 O/ , , ) of the total polygalacturonic acid trans-eliminase is present in the culture fluid during the exponential growth-phase of Erwinia carotovora. The enzyme may be regarded as an exoenzyme. The exact location of polygalacturonic acid transeliminase in the cells was not established; it could be truly intracellular or reside between the cell-wall and membrane.Glucose-grown cultures of Erwinia carotovora, strain ICPB-ECl53, do not elaborate detectable quantities of polygalacturonic acid trans-eliminase (E.C. 4.2.99.3) into the culture supernatant medium [I]. However, glucose-grown cells readily adapt to polygalacturonic acid utilization and produce a soluble intracellular and an extracellular enzyme. Both enzymes have been partially purified and appear to be identical [ 2 ] . One of the cultures used in the present study, ICPB-ECl53, is known to produce in addition to polygalacturonic acid trans-eliminase two other pectic enzymes, a hydrolytic polygalacturonase [3], and an oligogalacturonide trans-eliminase [4] ; we shall not deal further here with these two enzymes. The present investigation seeks to establish some of the factors controlling the synthesis of polygalacturonic acid trans-eliminase.
MATERIALS AND METHODSBacterial Cultures The following cultures of Erwinia spp. were used in this study: Erwinia carotovora ICPB-EC153, Erwinia aroideae ICPB-EA144, and Erwinia aroideae ICPB-EAl3. All were obtained from the International Collection of Phytopathogenic Bacteria (ICPB, Department of Bacteriology, University of California, Davis, California 95616, U.S.A.).
Cultural NethodsThe latter two cultures were obtained from a lyophilised state, suspended in nutrient broth, reisolated from yeast-glucose-CaCO, plates and maintained on yeast-glucose-CaCO, agar slants a t 4" for three weeks before the experiment. Erwinia carotovora ICPB-EC153 had been maintained on yeast-glucose-CaCO, medium for 1 year. This culture was grown on sterile potato slants (every 3 months), streaked on yeastglucose-CaCO, plates, and a single pectinolytic colony (calcium pectate plate test) reisolated and purified.The organisms were grown in an ammonium-salts mixture (basal medium) containing 1.0 g KC1, 0.2 g MgCI,, 7.0 g K,HP04, 5.4g KH,PO,, 1.Og (NH4),S04, 5 mg CaCl,, 0.6 mg FeSO, 7H,O and substrate (as required) per litre. The basal medium was autoclaved a t 121" for 15 min. The substrates were glucose, polygalacturonic acid (Sunkist Growers, No. 491), and glycerol. One percent solutions of these materials were sterilized by filtration through Millipore HA me...