Significant expression of functional human type 1 mitochondrial ADP/ATP carrier in yeast mitochondria

As a first step to characterize the unknown functional properties of the hu man mitochondrial ADP/ATP carrier (AAC), we tried to express human type I A AC (hAACI) in Saccharomyces cerevisiae. Expression of hAACI in yeast mitoch ondrial membrane was very low, although its transcript level was high. Its expression was improved greatly by replacement of its N-terminal region wit h the corresponding region of yeast type 2 AAC (yAAC2), as observed with th e bovine type 1 AAC (bAAC1). This chimeric hAAC1 showed similar ADP transpo rt activity to that of chimeric bAAC1, corresponding to the transport activ ity of bAAC1 in bovine heart mitochondria. These results suggested that the N-terminal region of yAAC2 is important for expression of the mammalian ca rriers in yeast mitochondria. Using the present expression system, studies on the functional properties of the human AAC isoforms in relation to their structures are now possible.