The interactions of tropolone with magnesium ions and tubulin

Tropolone, a simple analog of colchicine, interacts with Mg²⁺ with the formation of a 1:1 complex and an apparent equilibrium binding constant K_b of 1.4 · 10⁴ M^?1 in neutral aqueous solution at 25°C. The tropolone-Mg²⁺ complex, but not tropolone, is fluorescent. Since tubulin binds Mg²⁺ (Frigon, R.P. and Timasheff, S.N. (1975) Biochemistry 14, 4567–4573), previous reports of tropolone interaction with tubulin in Mg²⁺-containing buffers must be critically re-examined. Fluorescence and difference absorption spectroscopy experiments performed at essentially constant Mg²⁺ activity indicate that tubulin does bind tropolone, but the optical effects are too weak to use in quantitative studies.     

Studies on antigenic variability of C strains of foot-and-mouth disease virus by means of synthetic peptides and monoclonal antibodies.

Peptides representing the sequence of the immunodominant loop of foot-and-mouth disease virus strain C-S8 (YTASARGDLAHLTTTHARHLP, residues 136-156 of VP1) and of several variant viruses have been prepared by solid phase methods. In addition, five peptides with single-residue replacements at Leu147 (Ile, Nle, Val, Ala, Gly) have been synthesized. Tosyl and dinitrophenyl protections for histidine have been compared, the latter being found to give better synthetic products. The peptides have been tested in an immunodot assay against a panel of monoclonal antibodies directed towards the VP1 loop. Immunochemical results are discussed on the basis of the mobility of the region reproduced by the peptides and the nature of the side chain of residue 147.     

Induction of Tk polyagglutination by Bacteroides fragilis culture supernatants. Associated modifications of A B H and I i antigens

Tk transformed red blood cells were obtained in vitro by treatment with supernatants from cultures of three different Bacteroides fragilis strains. The reactions of these cells with AB sera show that Tk is different from other known types of polyagglutination. Beside the already known modifications of A B H antigens, we found that Tk activated cells have an important modification of I and i antigens: both are reduced, and can even be completely destroyed.     

Association of acquired polyagglutinabilities of types T and B. An observation]

Although T and acquired B polyagglutinabilities are not exceptional, simultaneous occurence of the two types is a rarer phenomenon. Ten days after an open heart surgery operation, the patient, age 55, had an infectious syndrom : two strains, Clostridium perfringens and Peptococcus variabilis were isolated. Simultaneously, her red cells were found to be polyagglutinable. The association of T and acquired B polyagglutinabilities could be demonstrated by serological studies of the patient's red cells, and by in vitro transformation of normal red cells using culture supernatants obtained from the two isolated strains.     

Solid-phase synthesis of PYLa and isolation of its natural counterpart, PGLa [PYLa-(4-24)] from skin secretion of Xenopus laevis

From the nucleotide sequence of clones isolated from a cDNA library constructed from skin of Xenopus laevis, the existence of PYLa, a peptide comprised of 24 amino acids, was predicted. This peptide was synthesized by solid-phase methods and purified to homogeneity with an overall yield of 61%. The synthetic peptide was used as reference substance to search for its natural counterpart in skin secretion of Xenopus. Two peptides were found which were very similar to PYLa except for the absence of the first three amino acids. These 21-amino-acid peptides, termed PGLa, can be generated from PYLa by cleavage after the single arginine residue present in the latter. The two forms of PGLa differ in their retention time on HPLC but have identical amino acid compositions and terminal sequences. Tryptic hydrolysis of synthetic PYLa after the single arginine yields exclusively PGLa with the shorter retention time on HPLC. The chemical difference between the two forms of PGLa is currently not known. The possible biological role of these newly discovered constituents of frog skin secretion is discussed.