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R D Zeikus

Publications and source records attributed to R D Zeikus.

6 recordsLinked to original sources
PubMed1985

Conus geographus toxins that discriminate between neuronal and muscle sodium channels.

We describe the properties of a family of 22-amino acid peptides, the mu-conotoxins, which are useful probes for investigating voltage-dependent sodium channels of excitable tissues. The mu-conotoxins are present in the venom of the piscivorous marine snail, Conus geographus L. We have purified seven homologs of the mu-conotoxin set and determined their amino acid sequences, as follows, where Hyp = trans-4-hydroxyproline. GIIIA R.D.C.C.T.Hyp.Hyp.K.K.C.K.D.R.Q.C.K.Hyp.Q.R.C.C.A-NH2 [Pro6]GIIIA R.D.C.C. T.P.Hyp.K.K.C.K.D.R.Q.C.K.Hyp.Q.R.C.C.A-NH2 [Pro7]GIIIA R.D.C.C.T.Hyp.P.K.K.C.K.D.R.Q.C.R.Hyp.Q.R.C.C.A-NH2 GIIIB R.D.C.C.T.Hyp.Hyp.R.K.C.K.D.R.R.C.K.Hyp.M.K.C.C.A-NH2 [Pro6]GIIIB R.D.C.C.T.P.Hyp.R.K.C.K.D.R.R. C.K.Hyp.M.K.C.C.A-NH2 [Pro7]GIIIB R.D.C.C.T.Hyp.P.R.K.C.K.D.R.R.C.K.Hyp.M.K.C.C.A-NH2 GIIIC R.D.C.C.T.Hyp.Hyp.K.K.C.K.D.R.R.C.K.Hyp.L.K.C.C.A-NH2. Using the major peptide (GIIIA) in electrophysiological studies on nerve-muscle preparations and in single channel studies using planar lipid bilayers, we have established that the toxin blocks muscle sodium channels, while having no discernible effect on nerve or brain sodium channels. In bilayers the blocking kinetics of GIIIA were derived by statistical analysis of discrete transitions between blocked and unblocked states of batrachotoxin-activated sodium channels from rat muscle. The kinetics conform to a single-site, reversible binding equilibrium with a voltage-dependent binding constant. The measured value of the equilibrium KD for GIIIA is 100 nM at OmV, decreasing e-fold/34 mV of hyperpolarization. This voltage dependence of blocking is similar to that of tetrodotoxin and saxitoxin as measured by the same technique. The tissue specificity and kinetic characteristics suggest that the mu-conotoxins may serve as useful ligands to distinguish sodium channel subtypes in different tissues.

Amino Acid Sequence↗
PubMed1985

A toxic thionin from Pyrularia pubera: purification, properties, and amino acid sequence.

A low-molecular-weight cytotoxic protein has been purified from Pyrularia pubera Michx. (Santalaceae). By comparison with the behavior of proteins of known molecular weight during Sephadex G-75 gel filtration and denaturing electrophoresis, a molecular weight of somewhat less than 6000 is indicated. Purification involves ammonium sulfate fractionation followed by either gel filtration on Sephadex G-75 or separation on a carboxymethyl cellulose CM52 column. At concentrations of 0.04 mg/ml the protein causes visible disruption of cultured mouse B16 melanoma cells. The complete amino acid sequence has been determined. The toxin contains 47 amino acids arranged as follows:Lys-Ser-Cys-Cys-Arg-Asn-Thr-Trp-Ala-Arg-Asn-C ys-Tyr-Asn-Val-Cys-Arg-Leu-Pro-Gly-Thr-Ile-Ser-Arg-Glu-Ile-Cys-Ala-Lys- Lys-Cys-Asp-Cys-Lys-Ile-Ile-Ser-Gly-Thr-Thr-Cys-Pro-Ser-Asp-Tyr-Pro-Ly s-OH. The protein is clearly a thionin, as shown by its close resemblance to the thionins from wheat and barley, to the viscotoxins from mistletoes, and to crambin.

Amino Acid Sequence↗
PubMed1984

Structural characterization of the isoforms of neonatal and adult rat liver metallothionein.

Metallothionein was purified from the livers of adult and neonatal rats. The complete amino acid sequences of isoforms I and II of Cd-induced adult metallothionein were determined by automated Edman degradation of CNBr and tryptic peptides of carboxymethylated proteins. Both isoproteins contain 61 residues, but differ at 12 of those positions. The positions of the 20 cysteinyl residues are invariant with respect to those in other known mammalian metallothioneins. Based on the following criteria, the two soluble and constitutive Zn-metallothionein isoforms from neonatal liver appear identical to their corresponding forms in the adult animal: 1) they behave identically on reverse-phase high-pressure liquid chromatography, anion-exchange chromatography and nondenaturing gel electrophoresis; 2) their amino acid compositions are the same within experimental error; and 3) their amino acid sequences are identical in the first 23 residues, even though isoforms I and II differ in 7 of those positions. It appears highly likely that isoforms from both neonatal and adult rats are encoded by the same genes, and therefore that the large age-dependent concentration differences seen in the liver must be due to variation in gene regulation.

Age Factors↗