Intracellular inorganic carbon exists as protein carbamate in photosynthesizing Euglena gracilis z.

The form of inorganic carbon accumulated in Euglena gracilis cells was determined. Euglena cell protein bound 0.96 nmol CO2/mg protein. The binding of CO2 was by the formation of protein carbamate as indicated by acid lability of the protein-CO2 complex, stimulation of complex formation by high ionic strength and the carbamate resonance in 13C-NMR spectrum. The protein carbamate could also be isolated from photosynthesizing Euglena. The formation of the carbamate required light energy fixed photosynthetically.