The group of De Duve first described the isolation of peroxisomes from rat liver tissue. These organelles can be separated from other sub-cellular organelles, such as lysosomes and mitochondria, because of their relatively high equilibrium density in sucrose (approx 1.24 g/cm3 ). The isolation of peroxisomes from the yeast Saccharomyces cerevisiae , however, has been hampered by the fact that under standard growth conditions peroxisomes are present in low numbers. Also, the lability of peroxisomes in general has complicated their purification.