Abstract
The electron transport system of autotrophically grown Alcaligenes eutrophus H16 has been investigated by spectroscopic and thermodynamic approaches. The results have been interpreted as evidence that isolated membranes contain a branched respiratory chain composed of three c-type haems (E m,7=+160 mV, + 170 mV, and + 335 mV), five b-type haems (E m,7=+ 5 mV, + 75 mV, + 205 mV, + 300 mV, and + 405 mV), two (possibly three) a-type haems [E m,7= + 255 mV, + 350 mV, (+ 420 mV)], and nne d-type haem. EPR-analysis of the signals at g=1.93, g=2.02, and g=1.90 revealed the presence of iron-sulphur centres diagnostic of complexes I (NADH dehydrogenase), II (succinate dehydrogenase), and III (ubiquinol/cytochrome c oxidoreductase). The low potential b haems (+ 5 mV and + 75 mV) plus the Rieske protein (g=1.90, E m,7=+ 280 mV), thought to be part of an orthodox bc 1 complex, were present in low amounts as compared to their counterparts in membranes from Paracoccus denitrificans. CO-difference spectra in the presence of either succinate, NADH, hydrogen, ascorbate/TMPD, and/or dithionite as reductants, suggested the existance of four different oxidases composed by bo-, cb-, a-, and d-type haems. It is concluded that in contrast to other chemolithotrophes, e.g. P. denitrificans, autotrophic growth of Alcaligenes eutrophus utilizes a respiratory system in which the bc 1 complex containing pathway is only partially involved in electron transport.
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