Guanosine triphosphate (GTP): the major organic phosphate in the erythrocytes of the elasmobranch Mustelus canis (smooth dogfish).

1. Ion exchange column chromatography of red cell extracts from the smooth dogfish (Mustelus canis) reveals a phosphate pool which includes inorganic phosphate, AMP, ADP and ATP. 2. GTP and an iron complex of this nucleotide (Fe-GTP) account for approximately 40% of the principal organic phosphates. 3. ATP accounts for 30%, and AMP and ADP approximately 10% each. 4. 2,3-DPG is not detectable by either enzymatic or chromatographic analysis. 5. The use of a "purified" buffer system consisting of redistilled formic acid and de novo synthesized ammonium formate increases the ratio of GTP to Fe-GTP from approximately 1.4:1 to 10:1. This suggests that all of the iron nucleotide complexes (ATP and GTP) previously reported in red cells may not represent a normally occurring intraerythrocyte complex.