Figure 3. Activation by calcium of ATP uptake.

Mitochondria (2 mg of protein/ml) from wild-type cells were incubated with [³H]ATP (A) or unlabelled ATP (B) for 5 min at 30 °C and the indicated calcium concentrations. ATP influx in (A) was corrected for external ATP with [¹⁴C]sucrose. The content of ATP+ADP in (B) was determined enzymatically. Results are means±S.E.M. for three independent experiments (A) and for a representative experiment performed in triplicate (B). (C) Alignment of the four putative EF-hand domains in Sal1p, SCaMC1, SCaMC2b, SCaMC3 and human calmodulin (GenBank® accession numbers P48233, AJ619987, AJ619990, AJ619988 and P02593 respectively). The alignment was carried out with the ClustalW program. The amino acids that contribute to the octahedral calcium co-ordination cage are labelled x, y, z, −x, −y and −z. The amino acids that do not satisfy the co-ordination bond of canonical EF-hands are in italic bold type.