Differential Synthesis of Five Primary Electron Transport Dehydrogenases in Hemophilus Parainfluenzae.

Growth of Hemophilus parainjluenzae requires the formation of an electron transport system consisting of six cytochrome components (1). As a compensatory mechanism for changing environment, this bacterium can modify the cytochrome oxidase composition and the proportions of the cytochromes during conditions where there is no cell division (2). The intact bacterium has remarkable permeability to many substrates that reduce the respiratory pigments and produce an oxygen uptake (3). n-Lactate, L-lactate, succinate, reduced diphosphopyridine nucleotide, and formate added to washed suspensions of this bacterium produce rapid rates of oxygen utilization (3). The dehydrogenases for these substrates are part of the membranebound electron transport system (3). Rupture of the bacteria with alumina releases the glycolytic enzymes and disrupts the respiratory activity produced by intermediates of the tricarboxylic acid cycle (3). The membrane fragments isolated from bacteria ruptured with alumina contain the substrate-stimulated oxygen uptake properties and the substrate-reducible dehydrogenases and cytochromes found in the intact cells (1, 3). This report presents evidence indicating that each of these five substrates reduces a distinct membrane-bound dehydrogenase, that these dehydrogenases are very likely flavoproteins, and that each dehydrogenase can be formed differentially during different growth conditions. The great variability in the composition of the cytochrome and flavoprotein components of the electron transport systems during conditions of limited net growth suggests that each respiratory pigment is added individually to the membrane.