Carotenes and retinal in Phycomyces mutants.

Three different types of beta-carotene mutants of Phycomyces have been studied. In 2 mutants (Type I) beta-carotene is still the principal carotene but scaled down or up relative to wild type. The carotene mixture of 2 mutants (Type II) consists mainly of phytoene and phytofluene. In Type III (2 mutants) beta-carotene is replaced by lycopene. The examination of the mutants reveals that the receptor pigment is very likely neither beta-carotene nor retinal. Transmission spectra through the growing zone of live sporangiophores of 1 of these mutants which contains less than one-thousandth of the beta-carotene content of wild type show that the receptor pigment extinction is less than 0.003 at its maximum.