ANTI-BIOTIN ANTIBODIES OFFER SUPERIOR ORGANELLE-SPECIFIC LABELING OF MITOCHONDRIA OVER AVIDIN OR STREPTAVIDIN

The mitochondrial matrix contains endogenously biotinylated proteins. These proteins can cause unexpected background signal when biotin-avid in-or biotin-streptavidin-based detection systems are used in immunocy tochemistry. Here we show that this reactivity can be deliberately exp loited, using a simple anti-biotin reagent, to obtain strong and highl y specific labeling of mitochondria by both light and electron microsc opy. The signal is substantially stronger than when either avidin or s treptavidin is used to detect the endogenous biotin. These results con firm the accessibility of protein-bound endogenous biotin to exogenous probes, and localize the biotinylated enzymes to the mitochondrial ma trix.