Background Owing to the ease of genetic manipulation and its im-

and death of the cell. They participate in key metabolic reactions, synthesize the majority of ATP in a cell, and regulate a number of signaling cascades, including apop-tosis [1]. ATP synthesis is vital for various biological re-actions. Many studies have measured ATP content or qualitative changes in total cellular ATP production, but few have quantified ATP production from oxidative phosphorylation of isolated mitochondria [2]. portance for bio-industry, the budding yeast Saccharo-myces cerevisiae is an ideal organism for the study of many basic cellular mechanisms in eukaryotic cells. Their organelles can be rapidly enriched in sufficient quantities for the analysis of specific functions such as metabolite or protein transport. Therefore, S. cerevisiase is a valuable model cell for studying the molecular and cellular mechanisms underlying the essential biological functions of mitochondria. However, mitochondrial pro-teins have many subunits, the functions of which are still largely unknown because a method for easy mutational analysis and sensitive assay development is still lacking [3]. One of the biggest problems is that the fractionatio