The amino acid sequence of GTP:AMP phosphotransferase from beef‐heart mitochondria

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Abstract
The amino acid sequence of GTP:AMP phosphotransferase (AK3) from beef-heart mitochondria was determined, except for 1 segment of .apprx. 33 residues in the middle of the polypeptide chain. The established sequence was unambiguously aligned to the sequence of cytosolic ATP:AMP phosphotransferase (AK1) from pig muscle, allowing for 6 insertions and deletions. With 30 of all aligned residues being identical, the homology between AK3 and AK1 is well established. As derived from the known 3-dimensional structure of AK1, the missing segment is localized at a small surface area of the molecule, far apart from the active center. The pattern of conserved residues demonstrates that earlier views on substrate binding have to be modified. The observation of 3 different consecutive N-termini indicates enzyme processing.