Carbon Dioxide Requirement and Nucleic Acid Metabolism of HeLa and Conjunctival Cells. ∗

Summary

Over 90% of C¹⁴ fixed by HeLa or conjunctival cells growing in a trisbuffered nutrient medium containing 5 micro-curies of NaHC¹⁴O₃ per 10 ml was recovered in the acid soluble and nucleic acid fractions. Most of this activity was found associated with the purines and the pyrimidines of such cells. The ribonucleosides were partially effective as a substitute for CO₂ in supporting cell multiplication. A combination of ribosides and oxaloacetate provided conditions as good as or better than CO₂ for multiplication of CO₂-depleted conjunctival cells. It may be concluded that, under the described experimental conditions, the chief functions of CO₂ in human cells are to provide specific precursors for syntheses of the purines, the pyrimidines and oxaloacetate.