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Figure 48.13 Oxygen-Binding Adaptations Myoglobin and the different hemoglobins have different O2-binding properties adapted for different circumstances. Fetal hemoglobin, for example, has a higher affinity for O2 than does adult hemoglobin, facilitating O2 transfer in the placenta. When high metabolism lowers the pH of the blood, or low O2 increases bisphosphoglyceric acid (BPG), hemoglobin releases more of its O2.