Reaction Kinetics of the Cytochrome System

Abstract

IN living wheat roots three cytochromes cooperate, the prosthetic groups of which correspond spectroscopically to the types a (= cytochrome oxidase), c and b of animal preparations. Succin-oxidase is the main dehydrogenase system¹. A factor X, characterized by a strong band at 570–575 mµ, is probably linked between succindehydrogenase and cytochrome b ^1,2. Studies of the time-course of oxidation, performed by means of a new automatic spectrophotometric technique¹, show a direct electron transference in the sequence succindehydrogenase ⇀ X ⇀ b ⇀ c ⇀ a ⇀ oxygen. The process of oxidation of the reduced cytochromes is a first-order reaction in accordance with the overall formula Fe²⁺ → Fe³⁺ + e. The molar velocity of oxidation, calculated as (½t is time in seconds for the half-way point of oxidation, c is relative molar concentration), shows very similar values for all cytochromes (see table), a fact compatible with a uniform electron transference between the reacting cytochromes, these probably being located in a fairly compact structural unit near the surface of the cells (cf. ref. 1).