Figure 1.

Cyr1 and PDE activities are present in mitochondria from S. cerevisiae. A) Whole cell (WC) fractionation into postmitochondrial supernatant (PMS), which mostly contains soluble cytoplasmic proteins, and mitochondria-enriched fraction (Mit), was performed as explained in Materials and Methods. Highly purified mitochondria (HP-Mit) were obtained by a Nicodenz gradient fractionation of the crude mitochondrial fraction. Pgk1 (3-phosphoglycerate kinase) is a cytoplasmic marker; Pma1 is a plasma membrane H⁺-ATPase; and Sec61 is a subunit of the endoplasmic reticulum protein translocation channel. B) Adenylyl cyclase activity, measured in purified yeast mitochondrial fractions over 30 min in the presence of 10 mM Mg²⁺-ATP, 100 mM Tris-HCl (pH 7.5), and the indicated concentration of bicarbonate. C) PDE activity in mitochondrial lysates, estimated by measuring the depletion of 28 pmol/ml of exogenously added cAMP, in the presence or absence of sodium bicarbonate. D) Adenylyl cyclase activity, measured in purified yeast mitochondrial fractions over 30 min in the presence of 10 mM Mg²⁺-ATP, 100 mM Tris-HCl (pH 7.5), 40 mM bicarbonate, and the indicated concentrations of KH7 and MDL-12330A .