Quinones in plant plasma membranes -: a missing link?

The occurrence of a vitamin-K-like substance (naphthoquinone group) and flavins (flavin mononucleotide and flavin adenine dinucleotide) is demonstrated in plasma membranes isolated from maize (Zea mays L.) roots, on the basis of high-pressure liquid chromotography and spectral analysis. At least three NAD(P)H dehydrogenases could be purified to homogeneity from this plant material, Two of these proteins (25 and 30 kDa) reduce hexacyanoferrate III and quinones, while the third (41 kDa) reduces oxalacetic acid but not hexacyanoferrate III in the presence of NADH. Low-temperature spectra demonstrate the occurrence of a h-type cytochrome in plasma membranes isolated from maize roots. The latter compound could be reduced by ascorbic acid (E-0' > +80 mV) and shows an alpha-band maximum at 559 nm (at -196 degrees C). NADH-dependent cytochrome b reduction could be observed only in the presence of detergent and increased after preincubation with vitamin K-3 (menadione). On the basis of the presented data a possible function of naphthoquinones in plasma membrane electron transfer is discussed.