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2.B.2 The Monensin (Monensin) Family

Monensin A and B are two polyketide antibiotics synthesized by Streptomyces cinnamonensis. They insert into membranes and exert their toxic effects by transporting monovalent ions (K+, Na+ and H+) across biological membranes in an electroneutral exchange process, thus collapsing individual ion gradients without dissipating the membrane potential. Na+ is strongly preferred to K+. Thus, Na+:H+ antiport is the favored reaction. Recently monensin has been shown to also mediate the rapid selective transport of lead (Pb2+) (Hamidinia et al., 2002).

The generalized reaction catalyzed by monensins is:

C1+ (in) + C2+ C1+ (out) + C2+ (in)

References associated with 2.B.2 family:

Eisenman, G., G. Szabo, S.G.A. McLaughlin, and S.M. Ciani. (1973). Molecular basis for the action of macrocyclic carriers on passive ionic translocation across lipid bilayer membranes. Bioenergetics 4: 93-148. 4717529
Hamidinia, S.A., O.I. Shimelis, B. Tan, W.L. Erdahl, C.J. Chapman, G.D. Renkes, R.W. Taylor, and D.R. Pfeiffer. (2002). Monensin mediates a rapid and selective transport of Pb2+. Possible application of monensin for the treatment of Pb2+ intoxication. J. Biol. Chem. 277: 38111-38120. 12080080
Harold, F.M., K.H. Altendorf, and H. Hirata. (1974). Probing membrane transport mechanisms with ionophores. Annals N.Y. Acad. Sci. 235: 149-160. 4527943
Hutchinson, C.R. (1999). Commentary. Microbial polyketide synthases: more and more prolific. Proc. Natl. Acad. Sci. USA. 96: 3336-3338.
Liu, H.B. and K.A. Reynolds. (1999). Role of crotonyl coenzyme a reductase in determining the ratio of polyketides monensin A and monensin B produced by Streptomyces cinnamonensis. J. Bacteriol. 181: 6806-6813. 10542184