Department of Biochemistry, Iwate Medical University School of Dentistry
Abstract
Mycoplasmas depend on the host cells for various nutrients such as nucleic acid precursors and steroids. It has been mentioned that the acquisition of the nucleotides from the host cells is probably mediated through their own nucleases. However, in Mycoplasma salivarium, the existence of nuclease has not yet been known. In this study, we examined the nuclease activity in M. salivarium, and analyzed the properties of the enzyme. The Triton X-114 solubilized supernatant (Tx) obtained from lysate of M. salivarium was used for the enzymatic analysis. The nuclease activity was detected as a specific band of 25kDa by SDS-PAGE and the following in-gel digestion (SDS-PAGE nuclease assay). The nuclease activity of Tx was strictly dependent on Ca^. The nuclease was heat-stable, and the optimum pH was in the range of 7-9. The nuclease showed a low substrate specificity. From these findings, it was revealed that M. salivarium has a novel type of 25kDa and Ca^ dependent nuclease. Moreover, we examined whether Tx could cleave the chromatin DNA in the nuclei originated from eukaryote cells. Consequently, Tx cleaved the DNA of HS-72 B cell nuclei in vitro. From these results, it has been suggested that M. salivarium in the host cells, obtains nucleotides by the digestion of DNA and RNA from the host cells with their own nuclease, and these cleavage results in injury in host cells and the following various pathogenesis of the oral region
