In 1971, Akira Endo, a Japanese biochemist working for the pharmaceutical company Sankyo, began to investigate this problem. Research had already shown cholesterol is mostly manufactured by the body in the liver with the enzyme HMG-CoA reductase. Endo and his team reasoned that certain microorganisms may produce inhibitors of the enzyme to defend themselves against other organisms, as mevalonate is a precursor of many substances required by organisms for the maintenance of their cell walls or cytoskeleton (isoprenoids). The first agent they identified was mevastatin (ML-236B), a molecule produced by the fungus "Penicillium citrinum".