Differential Inhibition of Phytoene Desaturases from Diverse Origins and Analysis of Resistant Cyanobacterial Mutants

Abstract

Recent work on the molecular biology of carotenogenic genes and enzymes showed that there are two different and unrelated types of phytoene desaturase. One can be found in bacteria and fungi whereas the other is present in cyanobacteria, algae, and higher plants. Studies with herbicidal inhibitors showed that only the latter type of enzyme is affected by the bleaching herbicides norflurazon, fluridone, and flurtam one. I50 values have been determined for inhibition of phytoene desaturase in either solubilized membranes of the cyanobacterium Synechococcus, membrane preparation of E. coli in which the corresponding gene from Synechococcus was expressed or purified and reactivated phytoene desaturase from this E. coli transformant. The values differ by two orders of magnitude. The importance of the lipid environment of the integral membrane protein phytoene desaturase for its interaction with herbicides has been discussed. With the purified phytoene desaturase it could also be shown that the pyrimidine derivative J852 which is an inhibitor of ζ-carotene desaturase also inhibits phytoene desaturase with an I50 value which is about 2700 times higher than for inhibition of phytoene desaturation.