We purified a mitochondrial GTP-binding protein, MTG33, from a particulate fraction of Ehrlich ascites tumor cells [Takeda, S., Sagara, Y., Kita, K., Natori, S., and Sekimizu, K. (1993) J. Biochem. 114, 684-690]. In the present work, three GTP-binding proteins, p23A, p23B, and p26, were purified from the same material. The Kd values of p23A, p23B, and p26 for GTP were 19, 6.8, and 4.0 nM, respectively. Binding of [alpha-32P]GTP to these proteins was inhibited by GTP and GDP, but not appreciably by other nucleotides such as ATP, CTP, UTP, and GMP. p23A, p23B, and p26 hydrolyzed GTP to GDP as well as MTG33 did. Peptide mapping analyses revealed that these GTP-binding proteins share common primary structures with MTG33. The defined properties of the three proteins suggest structural and functional relations to MTG33, which is localized in mitochondria.