Necessity of iron for the alternative respiratory pathway in acanthamoeba castellanii

Immunological identification of the alternative oxidase of Acanthamoeba castellanii mitochondria

“…However, contrary to potato tuber mitochondria, where all of the alternative oxidase protein is synthesised de novo during ageing, polypeptides detected by immunoblotting with AOA antibodies seem to be present constitutively (although there are variations in expression levels) in the mitochondria of amoeba. This is consistent with our previous results showing that trophozoites of A. castellanii display activity of the CN‐resistant alternative pathway at all phases of growth [10].…”

“…Siedow, personal communication). Another intriguing property, that distinguishes amoeba alternative oxidase from the plant alternative oxidase, is that it is activated by purine nucleoside 5′‐monophosphates, but not by keto acids [4, 9, 10, 14, 15]. And again, also this phenomenon has been observed in the fungus N. crassa [19]and in the yeast P. stipitis [20].…”

“…Not in all aspects the amoeba CN‐resistant oxidase resembles the one in higher plants: while in higher plant mitochondria the alternative oxidase is stimulated by pyruvate [12, 13], there is no effect of pyruvate on the amoeba CN‐resistant oxidase, which, however, is strongly stimulated by the purine nucleoside 5′‐monophosphates AMP [4, 9, 10, 14], GMP (the lowest K m of stimulation) and IMP [15]. The same effect of purine mononucleotides on the activity of the alternative pathway was observed in other micro‐organisms such as Euglena gracilis [16], Moniliella tomentosa [17], Paramecium tetraurelia [18], Neurospora crassa [19]and Pichia stipitis [20].…”

“…The activity of this CN‐resistant oxidase decreases during transition from the exponential to the stationary phase of culture in amoeba trophozoites [4, 9, 10]and is strongly controlled by the availability of iron in the culture medium [10]. Our previous results show that, as in plant mitochondria [2], CN‐resistant respiration in amoeba mitochondria branches from the main respiratory chain at the level of the ubiquinone pool and the flow of electrons through this pathway is not coupled to oxidative phosphorylation [4].…”