Proton magnetic resonance studies of carbonic anhydrase. III. Binding of sulfonamides

Resonances of the histidine region of human carbonic anhydrase B have been studied by proton magnetic resonance spectroscopy in the presence of seven sulfonamide inhibitors. Results of difference spectroscopy and observation of the C-2 resonance of an additional titratable histidine in some of these spectra suggest a conformational change in the enzyme, while the large number of unaltered resonances indicates involvement of only a few residues. Inhibition of carbonic anhydrase by sulfonamides appears to involve: stabilization of an appropriately oriented initial complex by hydrophobic binding of the aromatic ring of the inhibitor to residues of the cavity forming the active site; ionization of the sulfonamido group, facilitated by its proximity to zinc; protonation and displacement of the high pH ligand to the metal controlling catalytic activity, thought here to be a histidine residue; and formation by the sulfonamido group of an ionic bond to zinc and a hydrogen bond to the hydroxyl group of serine or threonine. Diversity of spectra produced with various sulfonamides suggests that substituents on the ring and heteroatoms within the ring interact with additional groups at the active site. Increase in inhibitory potency appears to involve optimizing the number as well as the strength of these interactions. An upper limit for the dissociation rate of these complexes of 10 sec-1 was obtained.

13C NMR studies of the interaction of concanavalin A with saccharides

The binding of alpha- and beta-methyl-D-glucopyranoside and beta-(o-iodo-pheryl)-D-glucopyranoside to concanavalin A has been studied by carbon-13 nuclear magnetic resonance techniques. The kinetics and binding orientations of these saccharides relative to the transition metal ion site in the protein have been determined.

Binding of 13 C-enriched -methyl-D-glucopyranoside to concanavalin A as studied by carbon magnetic resonance

Binding of alpha-methyl-D-glucopyranoside, uniformly enriched with 14% (13)C, to zinc and manganese derivatives of concanavalin A at pH 5.6 was studied by pulsed Fourier transform carbon magnetic resonance techniques. Spin-lattice relaxation (T(1)) of the [(13)C]carbons of the sugar was measured in the absence and presence of the two transition metal derivatives of the protein. In the presence of the manganese derivative of concanavalin A, selective relaxation of the sugar carbons was observed. The values for T(1) reflect different distances between the carbons of the bound sugar and the manganese ion. Calculation of the distance between the manganese ion and each carbon of the sugar permit the 3-dimensional orientation of the bound sugar to be determined relative to the transition metal site in the protein. The results indicate that alpha-methyl-D-glucopyranoside binds to the protein in the Cl chair conformation with its 3- and 4- carbons closest to the manganese ion at a mean distance of 10 A.

Antiviral action of camptothecin

At a concentration of 10 mum, camptothecin inhibited vaccinia deoxyribonucleic acid (DNA) synthesis in HeLa cells. Inhibition of viral DNA synthesis was observed when the drug was added before infection or at 1 or 2 hr after infection. Inhibitory effects of camptothecin on vaccinia DNA synthesis could be reversed, even after exposure to the alkaloid for 2 hr. Viral DNA, isolated from vaccinia-infected, camptothecin-treated cells, displayed an altered sedimentation constant after alkaline sucrose density gradient centrifugation. Incorporation of uridine into vaccinia messenger ribonucleic acid was inhibited by camptothecin, but the activity of ribonucleic acid polymerase, as tested in isolated vaccinia cores, was not affected by the drug. Camptothecin had essentially no effect on replication of poliovirus in HeLa cells.

Chemosterilant action of anthramycin: a proposed mechanism

The activity of anthramycin and structurally related analogs as chemosterilants of the housefly, Musca domestica L., correlates closely with the action of these compounds as inhibitors of Escherichia coli RNA polymerase. Since inhibition of RNA polymerase by anthramycin reflects binding of this antibiotic to the DNA primer required for enzyme activity, we propose that the interaction of anthramycin with DNA may also account for its action as a chemosterilant.

Aurintricarboxylic acid: inhibitor of initiation of protein synthesis

Aurintricarboxylic acid prevents the attachment of bacteriophage messenger RNA to ribosomes. As a consequence, initiation of protein synthesis in cell-free extracts prepared from Escherichia coli or rabbit reticulocytes is inhibited at concentrations of dye that do not prevent chain extension. Its properties can be distinguished from other agents that inhibit protein synthesis, including sodium fluoride, cycloheximide, and pactamycin.

Structural basis for the inhibition of protein biosynthesis: mode of action of tubulosine

A structural model for the inhibition of protein biosynthesis was previously formulated on the basis of a topochemical analogy between the ipecac alkaloids and the glutarimide antibiotics. The structure of tubulosine satisfies the requirements of this model. The prediction that such a compound would exhibit amebicidal activity and act by selectively inhibiting the transfer reaction in protein biosynthesis is confirmed.

Studies of Blood Group Substances

Precipitating antisera to unmodified human Lea and Leb blood group substance were obtained by immunization of goats. The specificities of these antisera, as defined by inhibition with oligosaccharides of known structure and activity, are very similar to human isoantibodies.

Polysaccharide Antigens of Candida Cell Wall

Immunochemical studies of Candida cell wall have established that the mannan is the major antigen. There at least two serologic groups within C. albicans; group A mannan contains all the determinants present in group B plus additional determinants. C. tropicalis mannan is antigenically very similar to C. albicans group A mannan. Cross-reactions of anti-C. albicans group A serum with several mannose-containing fungal polysaccharides were studied.

Metabolic alkalosis, a specific effect of adrenocortical hormones

With appropriate balance experiments and skeletal muscle analyses, it was shown that: 1) Dogs placed on a potassium-restricted diet lost approximately 15% of their muscle cell potassium but did not develop alkalosis. 2) The administration of DCA, ACTH or cortisone to animals on a potassium-restricted diet evoked metabolic alkalosis which was sustained only as long as the hormones were administered. A prompt return to normal occurred despite continued potassium restriction. 3) Alkalosis induced by chloride withdrawal or by cortisone administration during complete sodium restriction was not associated with evidence of potassium loss. These findings indicate that the increase in the serum bicarbonate induced by the steroids is a relatively direct effect, one that cannot be dependably related in a reciprocal fashion to the associated losses of body potassium.