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Role of polyvalent anions in lysosomal heavy metal detoxification
Author(s) -
Roggenbeck Barbara Anne,
Mandal Prabir,
Ahearn Gregory
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a1236-c
Subject(s) - vanadate , vesicle , electrochemical gradient , antiporter , chemistry , atpase , bafilomycin , biophysics , biochemistry , biology , membrane , apoptosis , autophagy , enzyme
Crustacean hepatopancreatic lysosomes are organelles of heavy metal sequestration and detoxification. In this study hepatopancreatic lysosomal membrane vesicles (LMV) from the American lobster ( Homarus americanus ) were prepared by standard centrifugation methods and 65 Zn 2+ , 36 Cl − , and 35 SO 4 2− were used to characterize the transport processes responsible for vesicular accumulation of these ions. 65 Zn 2+ influx into LMV was a hyperbolic function of external [Zn] and followed Michaelis‐Menten kinetics (K m = 32 ±10 μM; J max = 21 ± 3 pmol/mg protein x sec). This transport was stimulated by 1 mM ATP and abolished by the simultaneous addition of 1 mM ATP + 250 μM vanadate. Thapsigargin (10 μM) was also a significant inhibitor of zinc influx, but not as effective as vanadate. Cadmium and copper were competitive inhibitors of 65 Zn 2+ influx (Cd 2+ K i = 68 ± 3 μM; Cu 2+ K i = 33 ± 2 μM). An outwardly‐directed proton gradient, in the absence of ATP, stimulated 65 Zn 2+ influx, while an inwardly‐directed proton gradient inhibited metal uptake. Vesicles loaded with SO 4 2− or PO 4 3− led to a 3‐fold greater steady‐state accumulation of Zn 2+ than similar vesicles loaded with mannitol, Cl − , or oxalate 2−. 35 SO 4 2− influx was a hyperbolic function of internal [Cl] and 36 Cl − influx appeared to occur by diffusion in the absence of an antiport substrate. These results suggest that 65 Zn 2+ influx occurred by a vanadate‐ and thapsigargin‐sensitive ATPase transporter that was stimulated by an outwardly‐directed proton gradient. Polyvalent inorganic anions (SO 4 2− and PO 4 3− ) associate with the metal inside the vesicles and may result in concretion formation through precipitation at appropriate vesicular pH. Supported by NSF grant IBN04‐21986.