GSAO, its metabolites GCAO and CAO, and PENAO trigger opening of the mitochondrial permeability transition pore. A. Structures of GSAO, its metabolites, and PENAO. L-Glutamyltransferase catalyses the hydrolysis of the peptide bond between GSAO's L-glutamic and cysteine residues, while a dipeptidase hydrolyses the peptide bond between GCAO's glycine and cysteine residues. PENAO is a cysteine mimetic of CAO. B. Mitochondrial transition pore opening triggered by GSAO, GCAO, CAO and PENAO. Rat liver mitochondria were incubated with 100 μM of the different compounds and swelling measured by decrease in light scattering at 520 nm over 30 min. The data points and error bars are the mean ± SD from 4 experiments (performed in duplicate with two different mitochondrial preparations).