Cell surface oxygen consumption by mitochondrial gene knockout cells

Abstract

Mitochondrial gene knockout (ρ 0) cells that depend on glycolysis for their energy requirements show an increased ability to reduce cell-impermeable tetrazolium dyes by electron transport across the plasma membrane. In this report, we show for the first time, that oxygen functions as a terminal electron acceptor for trans-plasma membrane electron transport (tPMET) in HL60ρ 0 cells, and that this cell surface oxygen consumption is associated with oxygen-dependent cell growth in the absence of mitochondrial electron transport function. Non-mitochondrial oxygen consumption by HL60ρ 0 cells was extensively inhibited by extracellular NADH and NADPH, but not by NAD +, localizing this process at the cell surface. Mitochondrial electron transport inhibitors and the uncoupler, FCCP, did not affect oxygen consumption by HL60ρ 0 cells. Inhibitors of glucose uptake and glycolysis, the ubiquinone redox cycle inhibitors, capsaicin and resiniferatoxin, the flavin centre inhibitor, diphenyleneiodonium, and the NQO1 inhibitor, dicoumarol, all inhibited oxygen consumption by HL60ρ 0 cells. Similarities in inhibition profiles between non-mitochondrial oxygen consumption and reduction of the cell-impermeable tetrazolium dye, WST-1, suggest that both systems may share a common tPMET pathway. This is supported by the finding that terminal electron acceptors from both pathways compete for electrons from intracellular NADH.