A Carotene Precursor: Its Proposed Structure and Place in Biosynthetic Sequence.

The isoprenoids, cholesterol and rubber, are known to arise from mevalonic (3,5-dihydroxy-3-methylvaleric) acid (5, 7). The same is true of carotenes (1, 6). Thus it has been found in this laboratory that mlevalonic acid is rapidly incorporated into carotenes and related compounds in the tonmato fruit (6). The hydrocarbon fraction of tomatoes previously incubated with 2-C'4-mevalonate contains radioactivity, however, not only in the known carotenes but also in a previously undescribed, colorless polyene which possesses absorption maxima at 208 my and 231 my. The high specific activity of this compound, which has been referred to as fraction II (6), suggests that it may be a precursor of carotenes. This paper reports further experiments pertaining to the identity of fraction IT and to its role in the biosylntlhesis of carotenoids.