Adenosine phosphorylase activity in a mutant Hep-2 cell line contaminated withmycoplasma hyorhinis

Summary Metabolic studies in HEp-2/MP,MIR cells (an adenosine kinase, hypoxanthine phosphoribosyltransferase negative mutant) indicated the presence of adenosine phosphorylase activity. This activity, unknown in established mammalian cell lines, resulted in the glycosidic cleavage of both adenosine and the antiviral drug arabinosyladenine. The activity was observed readily in the presence or absence of the adenosine deaminase inhibitor coformycin. Isopycnic separation of ³H]thymidine-labeled DNA species in CsCl density gradients resulted in the appearance of two distinct peaks. The heavier peak coincided with ¹⁴C]thymidine-labeled marker DNA of human origin, whereas the lighter peak was within the range associated with mycoplasmal DNA. Testing by commercial laboratories confirmed the presence of mycoplasma in HEp-2/MP,MIR cells. The contaminant was identified asMycoplasma hyorhinis, a porcine mycoplasma. Following γ-irradiation (3000 rads) to block cellular mitosis, the mycoplasma-contaminated HEp-2/MP,MIR cells were cocultivated with mycoplasma-free wild-type HEp-2 cells which did not exhibit adenosine phosphorylase activity. Following serial cocultivation in a medium designed to favor the survival of the wild-type cells, adenosine phosphorylase activity was found in the previously uninfected cells. Studies of this nature emphasize the need for investigators to carefully monitor their cell lines for mycoplasma. Presented at the 25th Annual Meeting of the Tissue Culture Association, Philadelphia, Pa., June 1976. This work was supported by Public Health Service Grants DE 02731 from the National Institute of Dental Research and CA 16219 from the National Cancer Institute.