Regulation of Acanthamoeba castellanii alternative oxidase activity by mutual exclusion of purine nucleotides; ATP's inhibitory effect.
The effects of different adenine and guanine nucleotides on the cyanide-resistant respiration (i.e. alternative oxidase (AcAOX) activity) of mitochondria from the amoeba A. castellanii mitochondria were studied. We found that guanine nucleotides activate AcAOX to a greater degree than adenine nucleotides, and that nucleoside monophosphates were more efficient activators than nucleoside di- or triphosphates. The extent of the nucleotides' influence on AcAOX was dependent on the medium's pH and was more pronounced at pH 6.8, which is optimal for AcAOX activity. In contrast to other purine nucleosides, we demonstrate, for the first time, that ATP has an inhibitory effect on AcAOX activity. Since we also observed the inhibition by ATP in the mitochondria of another protozoon, such as Dictyostelium discoideum, and the yeast, Candida maltosa, it may be a regulatory feature common to all purine nucleotide-modulated non-plant AOXs. The physiological importance of this discovery is discussed. Kinetic data show that the binding of GMP (a positive allosteric effector) and the binding of ATP (a negative allosteric effector) to AcAOX are mutually exclusive. ATP's inhibition of the enzyme can be overcome by sufficiently high concentrations of GMP, and conversely, GMP's stimulation can be overcome by sufficiently high concentrations of ATP. However, an approximately three times lower concentration of GMP compared to ATP gives a half maximal effect on AcAOX activity. This is indicative of a higher binding affinity for the positive effector at the same or, at least overlapping, nucleotide-binding sites on AcAOX. These results suggest that AcAOX activity in A. castellanii mitochondria might be controlled by the relative intracellular concentrations of purine nucleotides.
Woyda-Ploszczyca
Andrzej M
AM
Laboratory of Bioenergetics, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznan, Poland.
Sluse
Francis E
FE
Jarmuszkiewicz
Wieslawa
W
D048248:Acanthamoeba castellanii / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D002175:Candida / Q000187:drug effects / Q000201:enzymology; D019069:Cell Respiration / Q000187:drug effects; D003486:Cyanides / Q000494:pharmacology; D004023:Dictyostelium / Q000187:drug effects / Q000201:enzymology; D006157:Guanosine Monophosphate / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology; D024101:Mitochondrial Proteins; D008954:Models, Biological; D010088:Oxidoreductases / Q000037:antagonists & inhibitors*; D010766:Phosphorylation / Q000187:drug effects; D010940:Plant Proteins; D012995:Solubility / Q000187:drug effects; D013379:Substrate Specificity / Q000187:drug effects; D000099188:Alternative Oxidase
D000255:Adenosine Triphosphate; D003486:Cyanides; D006157:Guanosine Monophosphate; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase