EVIDENCE FOR THE ROLE OF NA-1( AND GALACTURONIC ACID IN THE REGULATION OF POLYGALACTURONASE PRODUCTION BY THE MARINE ANAEROBE, EUBACTERIUM SP STRAIN P)

Polygalacturonase (PG) [endo-, EC 3.2.1.15, plus exo-, EC 3.2.1.67 and EC 3.1.2.82] was examined in the marine anaerobic bacterium, Eubacter ium sp. strain P-1. Polygalacturonase was released principally into th e culture fluid and had pH and temperature optima of 5.0 and 30 degree s C, respectively. Galacturonides, chain length > 3 monomer units, tri - and digalacturonic acids, were the principal early products of PG ac tion (0 to 5 min) with the later formation of mono-galacturonic acid ( 5 to 15 min). Activities of PG up to 70 U mL(-1) (148 U mg protein(-1) ) were obtained in cultures grown on pectin at 3.0 mg mL(-1) but above this concentration, levels declined and galacturonic acid accumulated in the culture medium. When pectin was replaced as the growth substra te with galacturonic acid, cellobiose or starch, substantially lower a ctivities were obtained. The poor inducing properties of galacturonic acid together with its accumulation at elevated pectin concentrations, suggested that it suppressed PG production. This was confirmed when a ddition of the monomer to a pectin growth culture which had initiated PG production, resulted in the suppression of PG production, which res umed only when galacturonic acid was almost completely utilized. Salin ity also affected the production of PG with maximum levels occurring a t salinities of < 1 parts per thousand. Increasing salinity beyond thi s value led to a decline in activity. Ion substitution experiments ind icated that suppression of PG was due to increases in Na+ and not Cl-.