<P> Lysosomes should not be confused with liposomes, or with micelles . </P> <P> Christian de Duve, the chairman of the Laboratory of Physiological Chemistry at the Catholic University of Louvain in Belgium, had been studying the mechanism of action of a pancreatic hormone insulin in liver cells . By 1949, he and his team had focused on the enzyme called glucose 6 - phosphatase, which is the first crucial enzyme in sugar metabolism and the target of insulin . They already suspected that this enzyme played a key role in regulating blood sugar levels . However, even after a series of experiments, they failed to purify and isolate the enzyme from the cellular extracts . Therefore, they tried a more arduous procedure of cell fractionation, by which cellular components are separated based on their sizes using centrifugation . </P> <P> They succeeded in detecting the enzyme activity from the microsomal fraction . This was the crucial step in the serendipitous discovery of lysosomes . To estimate this enzyme activity, they used that of standardised enzyme acid phosphatase, and found that the activity was only 10% of the expected value . One day, the enzyme activity of purified cell fractions which had been refrigerated for five days was measured . Surprisingly, the enzyme activity was increased to normal of that of the fresh sample . The result was the same no matter how many times they repeated the estimation, and led to the conclusion that a membrane - like barrier limited the accessibility of the enzyme to its substrate, and that the enzymes were able to diffuse after a few days (and react with their substrate). They described this membrane - like barrier as a "saclike structure surrounded by a membrane and containing acid phosphatase ." </P> <P> It became clear that this enzyme from the cell fraction came from a membranous fractions, which were definitely cell organelles, and in 1955 De Duve named them "lysosomes" to reflect their digestive properties . The same year, Alex B. Novikoff from the University of Vermont visited de Duve's laboratory, and successfully obtained the first electron micrographs of the new organelle . Using a staining method for acid phosphatase, de Duve and Novikoff confirmed the location of the hydrolytic enzymes of lysosomes using light and electron microscopic studies . de Duve won the Nobel Prize in Physiology or Medicine in 1974 for this discovery . </P>

What does a lysosome look like in an animal cell