Discovering, counting, cataloguing proteins

Using 'quantitative mass spectrometry' and bioinformatics methods, a team from Warscheid's research group first determined the abundance of thousands of proteins in different cellular fractions of baker's yeast. A team from Wiedemann's research group then analyzed mitochondrial proteins using biochemical methods and microscopy. The resulting mitochondrial proteome comprises a total of 901 proteins, including 82 proteins not previously associated with mitochondria. For an additional 119 a mitochondrial localization had been ambiguous.

While humans require oxygen to breathe, yeast cells can either consume oxygen or use a different metabolic pathway called fermentation, a process well known for producing alcoholic beverages. The researchers cultured yeast cells in a fermentative or respiratory medium and determined that the shift from fermentative to respiratory conditions caused dramatic changes in the mitochondria: The amount of mitochondrial proteins in a single cell doubles and the enzymes required for respiration are even four times more abundant when growing in a respiratory medium.

The scientists further studied in which areas of the mitochondrion the various proteins are localized and how newly discovered proteins interact with other proteins in a network. Through this study the researchers have gained extensive data about the newly defined mitochondrial proteome of baker's yeast.