title: Interaction of heme and heme-hemopexin with an extracellular oxidant system used to measure cell growth-associated plasma membrane electron transport.
abstract: Since redox active metals are often transported across membranes into cells in the reduced state, we have investigated whether exogenous ferri-heme or heme bound to hemopexin (HPX), which delivers heme to cells via receptor-mediated endocytosis, interact with a cell growth-associated plasma membrane electron transport (PMET) pathway. PMET reduces the cell-impermeable tetrazolium salt, WST-1, in the presence of the mandatory low potential intermediate electron acceptor, mPMS. In human promyelocytic (HL60) cells, protoheme (iron protoporphyrin IX; 2,4-vinyl), mesoheme (2,4-ethyl) and deuteroheme (2,4-H) inhibited reduction of WST-1/mPMS in a saturable manner supporting interaction with a finite number of high affinity acceptor sites (Kd 221 nM for naturally occurring protoheme). A requirement for the redox-active iron was shown using gallium-protoporphyrin IX (PPIX) and tin-PPIX. Heme-hemopexin, but not apo-hemopexin, also inhibited WST-1 reduction, and copper was required. Importantly, since neither heme nor heme-hemopexin replace mPMS as an intermediate electron acceptor and since inhibition of WST-1/mPMS reduction requires living cells, the experimental evidence supports the view that heme and heme-hemopexin interact with electrons from PMET. We therefore propose that heme and heme-hemopexin are natural substrates for this growth-associated electron transfer across the plasma membrane.
authors.affiliation: School of Biological Sciences, University of Missouri-Kansas City, 5007 Rockhill Road, Kansas City, MO 64110-2499, USA.
authors.forename: Kimberly R
authors.initials: KR
authors.lastname: Rish
authors.forename: Ryan
authors.initials: R
authors.lastname: Swartzlander
authors.forename: Takrima N
authors.initials: TN
authors.lastname: Sadikot
authors.forename: Michael V
authors.initials: MV
authors.lastname: Berridge
authors.forename: Ann
authors.initials: A
authors.lastname: Smith
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D049109:Cell Proliferation; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D018922:HL-60 Cells; D006418:Heme / Q000737:chemistry*; D006466:Hemopexin / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D008956:Models, Chemical; D016877:Oxidants / Q000737:chemistry*; D010088:Oxidoreductases / Q000378:metabolism; D011524:Protoporphyrins / Q000737:chemistry
chemical_list: D016877:Oxidants; D011524:Protoporphyrins; D006418:Heme; D006466:Hemopexin; C028025:protoporphyrin IX; D010088:Oxidoreductases