Oxidation of Cytochrome 605 Is the Rate-Limiting Step when Ferrimicrobium acidiphilum Respires Aerobically on Soluble Iron

Abstract

The identities and functions of proteins involved in aerobic respiration on extracellular ferrous ions at acidic pH are poorly understood in the four phyla of Gram-positive eukaryotes and archaea where such activities occur. In situ absorbance measurements were conducted on Fm. acidiphilum as it respired on extracellular iron using an integrating cavity absorption meter that permitted accurate optical measurements in turbid suspensions of the intact bacterium under physiological conditions. The significance of these measurements is that they permitted a direct spectrophotometric examination of the extents and rates of biological electron transfer events in situ under noninvasive physiological conditions without disrupting the complexity of the live cellular environment. One thing is certain: one way to understand how a protein functions in an intact organism is to actually observe that protein as it functions in the intact organism. This paper provides an example of just such an observation.