A carotenogenic enzyme aggregate in Phycomyces: evidence from quantitive complementation.

Wild-type Phycomyces blakesleeanus accumulates beta-carotene, while the mutant strain C2 is unable to synthesize carotenoids, and the mutant strain C9 accumulates lycopene. Heterokaryons containing a proportion, p, of C2 nuclei and (l - p) of C9 nuclei accumulate lycopene, gamma-carotene, and beta-carotene in the relative amounts (l - p), p(l - p), and p(2), respectively, for different values of p. It is shown that these results are expected from the operation of a carotenogenic enzyme aggregate that works as an assembly line and contains two copies of a cyclase, which is defective in strain C9, as well as other enzymes.