title: Zinc inhibition of mitochondrial aconitase and its importance in citrate metabolism of prostate epithelial cells.
abstract: Prostate epithelial cells possess a uniquely limiting mitochondrial (m-) aconitase activity that minimizes their ability to oxidize citrate. These cells also possess uniquely high cellular and mitochondrial zinc levels. Correlations among zinc, citrate, and m-aconitase in prostate indicated that zinc might be an inhibitor of prostate m-aconitase activity and citrate oxidation. The present studies reveal that zinc at near physiological levels inhibited m-aconitase activity of mitochondrial sonicate preparations obtained from rat ventral prostate epithelial cells. Corresponding studies conducted with mitochondrial sonicates of rat kidney cells revealed that zinc also inhibited the kidney m-aconitase activity. However the inhibitory effect of zinc was more sensitive with the prostate m-aconitase activity. Zinc inhibition fit the competitive inhibitor model. The inhibitory effect of zinc occurred only with citrate as substrate and was specific for the citrate --> cis-aconitate reaction. Other cations (Ca2+, Mn2+, Cd2+) did not result in the inhibitory effects obtained with zinc. The presence of endogenous zinc inhibited the m-aconitase activity of the prostate mitochondrial preparations. Kidney preparations that contain lower endogenous zinc levels exhibited no endogenous inhibition of m-aconitase activity. Studies with pig prostate and seminal vesicle mitochondrial preparations also revealed that zinc was a competitive inhibitor against citrate of m-aconitase activity. The effects of zinc on purified beef heart m-aconitase verified the competitive inhibitor action of zinc. In contrast, zinc had no inhibitory effect on purified cytosolic aconitase. These studies reveal for the first time that zinc is a specific inhibitor of m-aconitase of mammalian cells. In prostate epithelial cells, in situ mitochondrial zinc levels inhibit m-aconitase activity, which provides a mechanism by which citrate oxidation is limited.
authors.affiliation: Cellular and Molecular Biology Section/Oral Craniofacial and Biological Sciences, Dental School, University of Maryland, Baltimore, Maryland 21201, USA. lcostell@umabnet.ab.umd.edu
authors.forename: L C
authors.initials: LC
authors.lastname: Costello
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.forename: R B
authors.initials: RB
authors.lastname: Franklin
authors.forename: M C
authors.initials: MC
authors.lastname: Kennedy
mesh_terms: D000154:Aconitate Hydratase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D002951:Citrates / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D007668:Kidney / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology; D011467:Prostate / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity; D015032:Zinc / Q000494:pharmacology*
chemical_list: D002951:Citrates; D000154:Aconitate Hydratase; D015032:Zinc