Cytochrome Components of Plant Microsomes

Abstract

The electron transport components of the microsomal fraction of cauliflower buds and mung bean hypocotyls were investigated using split‐beam and dual wavelength spectrophotometry under a variety of reducing conditions. Cauliflower microsomes were found to contain an ascorbate‐reducible component, termed cytochrome b‐559.5 [E′0=+ 135 ± 20 mV; λmax (reduced minus oxidised) = 559.5, 527 and 429 nm at 23 °C], cytochrome b5 [E'0=−20 ± 20 mV; λmax (reduced minus oxidised) = 556, 526 and 425 nm at 23°C], cytochromes P‐450 and P‐420. On the basis of binding studies with ethyl isocyanide, degradation of cytochrome P‐450 to P‐420, redox potential, aniline binding, and relative rates of reduction by NADPH and NADH, it is suggested that the cytochrome P‐450 system is analogous to that in mammalian microsomes. Other components, reducible only by dithionite, may also be present. Mung bean microsomes were found to contain an ascorbate‐reducible component, termed cytochrome b‐562 [E′0=+ 120 ± 20 mV; λmax (reduced minus oxidised) = 562, 528, and 430 nm at 23 °C], cytochrome b5, and a low potential component which was reducible only by sodium dithionite. No cytochrome P‐450 or P‐420 could be detected. A general method of analysis of the cytochromes was developed and applied to the microsomes from a variety of plant sources. The results indicate that large variations, both in type and amount of components, occur between the microsomes from different plant materials. Copyright © 1975, Wiley Blackwell. All rights reserved