Monensin A (I), a polyether antibiotic1) produced by Streptomyces cinnamonensis, is a natural ionophore specific for sodium ions2, 3). It is successfully used to control coccidiosis in poultry and to promote the growth of cattle. Studies employing 14C-labelled precursors have proved that molecule of I is assembled from five acetate, seven propionate, and one butyrate units4). According to a recent 13C NMR study5),
Human carbonic anhydrase IX (CA IX), a protein specifically expressed on the surface of solid tumour cells, represents a validated target both for anticancer therapy and diagnostics. We recently identified sulfonamide dicarbaboranes as promising inhibitors of CA IX with favourable activities both in vitro and in vivo. To explain their selectivity and potency, we performed detailed X-ray structural analysis of their interactions within the active sites of CA IX and CA II. Series of compounds bearing various aliphatic linkers between the dicarbaborane cluster and sulfonamide group were examined. Preferential binding towards the hydrophobic part of the active site cavity was observed. Selectivity towards CA IX lies in the shape complementarity of the dicarbaborane cluster with a specific CA IX hydrophobic patch containing V131 residue. The bulky side chain of F131 residue in CA II alters the shape of the catalytic cavity, disrupting favourable interactions of the spherical dicarbaborane cluster.
Although we correctly plotted and interpreted the data as first order, the units for the rate constants in Table 1 are labeled as second order rather than first order. The units should be "sec -1 " rather than "mol/L‚sec".
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