BIOCHEMICAL-STUDIES ON LEVJ, A FRUCTANASE FROM ACTINOMYCES-NAESLUNDIIT14V

The Actinomyces naeslundii T14V gene levJ encodes a sucrase with fruct anase activity and may be responsible for the fructanase activity obse rved bound to the surface of A. naeslundii T14V cells. A large proport ion of LevJ expressed in Escherichia coil was translocated to the peri plasm, and translocation and enzymatic activity were not affected by d eletion of a putative cell-wall anchor sequence. The pH optimum of the enzyme was found to be between 5.5 and 6.5 whether the substrate was sucrose or inulin, although inulinase activity was more sensitive than sucrose activity to perturbation of the pH from the optimum. The rela tion between LevJ inulinase activity and pH was similar to that of A. naeslundii whole cells. LevJ exhibited standard saturation kinetics wi th sucrose, and the K-m was calculated to be 89 mM, but it was not pos sible to calculate a K-m for inulin. Evidence for inhibition of inulin ase activity but not sucrase activity by high concentrations of inulin was obtained. Copyright (C) 1996 Elsevier Science Ltd.