PubMed Health⌕ Search

Biomedical subjects

V Renugopalakrishnan

Publications and source records attributed to V Renugopalakrishnan.

49 records · Page 3Linked to original sources
PubMed1985

Relative molecular mass determination of a major, highest relative molecular mass extracellular amelogenin of developing bovine enamel.

Proteins of developing bovine enamel were fractionated by molecular sieving and ion-exchange chromatography. The major fraction corresponding to the highest Mr amelogenin of Mr approximately 26 000-30 000 was isolated and its Mr determined by SDS-PAGE, molecular sieving on G-100 resin and high performance liquid chromatography and by sedimentation-equilibrium ultracentrifugation, the latter three procedures in guanidine hydrochloride. SDS-PAGE and HPLC molecular sieving, employing commonly used Mr standards, gave Mr values of approximately 22 000-26 000. SDS-PAGE and HPLC molecular sieving, using proline-rich CNBr peptides of collagen as standards, and sedimentation-equilibrium ultracentrifugation, gave Mr values of approximately 15 000-18 000 and approximately 17 385, respectively. These latter values correspond well with those reported earlier and with the Mr of the major amelogenin computed from recent amino acid sequence data (approximately 19 000). It is concluded that the recently described, highest Mr amelogenin of Mr = 26 000-30 000 is not a new component but is identical to the proline-rich components having relative molecular masses ranging from 15 000 to 18 000 described much earlier by several groups of workers.

Amelogenin↗
PubMed1985

Conformational states of Leu5- and Met5-enkephalins in solution.

The molecular conformations of Leu5- and Met5-enkephalins in aqueous and DMSO solutions were investigated by FT-IR and laser Raman spectroscopic methods. The amide I, II, and III regions in the FT-IR spectra of Leu5- and Met5-enkephalins in aqueous solution were analyzed by performing Fourier self-deconvolution of the bands. Leu5-enkephalin in aqueous solution is found to exist in both type II beta-turn and beta-sheet structures, whereas Met5-enkephalin has a lesser tendency to form beta-turn structure in aqueous solution. It is likely that these different conformers of enkephalins might bind to different receptor types.

Chemical Phenomena↗
PubMed1978

Proton magnetic resonance and conformational energy calculations of repeat peptides of tropoelastin. A permutation of the hexapeptide.

The conformation of a hexapeptide sequence occurring in tropoelastin is discussed from the results obtained using a combined approach of theoretical conformational energy calculations on HCO-Val-Ala-Prb-Gly-OMe and 1h nmr studies on t-Boc-Val-Ala-Pro-Gly-Val-Gly-OMe in a dilute solution of methanol. Both studies have reasonable concurrence with respect to the preferred conformation of the hexapeptide and an analysis of the combined results suggests that the hexapeptide is stabilized by a beta-turn involving the Ala1,iC=O and Val4,iNH groups and a gamma-turn involving Gly5,iC=O and Gly3,iNH groups. A weaker interaction between Gly3,iC=O and Gly5,iNH groups is also found to be possible. Conformational features of the first valyl residue in the sequence Val-Ala-Pro-Gly-Val-Gly and the last valyl residue in Ala-Pro-Gly-Val-Gly-Val are compared and found to have similar torsion angles. The implications of such a similarity are discussed with respect to the conformation of the polyhexapeptide.

Amino Acid Sequence↗
PubMed1978

A theoretical study of Na+ and Mg+2 binding to the carbonyl oxygen of N-methyl acetamide.

Molecular orbital calculations (CNDO/2) are reported for the interaction of Na+ and Mg+2 with the carbonyl of a model peptide moiety (N-methyl acetamide) as a function of the C--O ... Me distance and angle and with variation in the number of ligands for the purpose of determining the steepness of the distance dependence of the binding energy and for the purpose of determining the reduction of charge on the ion with increasing numbers of ligands. The greater energy derived on divalent ion binding and the steeper distance dependence indicate that selective, divalent over monovalent, ion binding will occur whenever the liganding system can provide a coordination shell of appropriate dimension. The calculations indicate that the preferred C--O ... Me angle is not 180 degrees. Of particular note is the decrease of charge on the cation on binding to N-methyl acetamide. One ligand bound to Na+ reduces the charge from 1.0 to 0.7 electron units and four ligands bound to Mg+2 reduces the charge from 2.0 to 0.7 electron units. This is of primary significance in carrier and channel mechanisms for cation permeation of lipid membranes; and although the numerical values are qualitative, the implication is for allowance of multiple occupancy of channels by monovalent cations.

Acetamides↗
PubMed1976

Energetics of the deformation of a peptide unit. Semi-empirical molecular orbital and ab initio study of N-methyl acetamide and N-acetyl-L-alanine N-methyl amide.

The problem of non-planarity of peptide unit has been investigated using N-methyl acetamide as a theoretical model. A semi-empirical molecular orbital method: Iterative Extended Hückel Theory viz. IEHT/2 (Adams S. (1974) Doctoral dissertation, State University of New York at Buffalo, U.S.A.) and non-empirical abinitio method with minimal basis set, STO-3G (Hehre, W.J., Stewart, R.F. and Pople, J.A. (1969) J. Chem. Phys. 51, 2657-2664) were used to probe the energetics of the distortion of a planar peptide unit. Distortion of one of the peptide units in a dipeptide, N-acetyl-L-alanine N-methyl amide has also been investigated using abinitio method. The studies amply demonstrate the possibility of the existence of a non-planar peptide unit. Distortion of about 10-15 degrees is predicted to bring about very small loss in energy. The results are substantiated by results from experimental studies.

Acetamides↗
PubMedDate not supplied

Glycine-extended anglerfish peptide YG (aPY) a neuropeptide Y (NPY) homologue may be a precursor of a biologically active peptide.

The 37 residue peptide YG (aPY), isolated from anglerfish endocrine pancreas, bears distinct sequence homology to the pancreatic polypeptide family of hormones. However, instead of a carboxyl-terminal tyrosine-amide, aPY has a free carboxyl-terminus ending with glycine. Towards studying the structure-activity relationship of this hormone, we have synthesized aPY by solid phase methodology using Boc-amino acid derivatives and phenylacetamidomethyl resin. The crude peptide was purified to homogeneity in 20% yield by reversed phase chromatography. The purified peptide had the expected amino acid composition and sequence, and was found to be identical with the natural aPY by analytical HPLC and peptide mapping of proteolytic digests. Neither the snythetic nor the natural aPY exhibited the characteristic vasoconstrictor activity of the related pancreatic polypeptide family of hormones. However, [Des37-Gly]-aPY, isolated from the anglerfish pancreas, caused vasoconstriction in rats. Based on these results and by analogy to the glycine-extended gastrin peptides, it may be suggested that aPY is a precursor of a biologically active peptide, namely [Des37-Gly]-aPY-amide.

Amino Acid Sequence↗
PubMedDate not supplied

Syntheses, structures and anorectic effects of human and rat amylin.

Amylin, a 37-residue polypeptide with a single disulfide bond originally isolated from the pancreas of type-II diabetic patients, has been shown to cause peripheral insulin resistance and to attenuate the inhibition of hepatic glucose output by insulin. We have also shown that amylin is present in the rat hypothalamus and that it inhibits food intake by rats. In order to further investigate the anorectic properties we synthesized both human and rat amylin by the solid phase method and purified to homogeneity in an overall yield of 10-20%. Structural analyses indicated that human amylin exhibited predominantly a beta-sheet structure at both acidic and alkaline pH, whereas no ordered structure was evident in the case of rat amylin. Intrahypothalamic injection of rat amylin resulted in a potent dose-dependent inhibitory effect on the food intake by rats adapted to eat their daily ration of food in an eight-hour period. Human amylin was less effective as an anorectic agent. Furthermore, rat amylin completely blocked the potent orexigenic effect of neuropeptide Y (NPY). These investigations show that there is a fundamental difference in the secondary structures of human and rat amylin and that rat amylin is a potent inhibitor of both basal and NPY-induced feeding by rats.

Amino Acid Sequence↗
PubMedDate not supplied

Dynorphin-phospholipid membrane interactions: role of phospholipid head-group and cholesterol.

The interaction of the kappa-opioid receptor-selective heptadecapeptide dynorphin A(1-17) (Tyr1-Gly-Gly-Phe-Leu5-Arg-Arg-Ile-Arg-Pro10-Lys-Leu-Lys-Trp-As p15-Asn-Glu) with phospholipid membranes has been investigated by monitoring the leakage of the internal aqueous contents of liposomes, the changes in the tryptophan emission spectrum, and the collisional quenching of tryptophan fluorescence by brominated lipids. The peptide induces more extensive leakage of contents from phosphatidylserine than from phosphatidylcholine vesicles, and experiences a blue shift of the Trp fluorescence emission maximum in the presence of phosphatidylserine vesicles. In the presence of phosphatidylcholine vesicles, however, the Trp fluorescence intensity is reduced without a blue shift. In phosphatidylserine membranes containing 10 mol% phosphatidylcholine, the intensity of the blue-shifted fluorescence is enhanced. This avid interaction of dynorphin A(1-17) with phosphatidylserine membranes is likely to be mediated by the positively charged Arg and Lys groups. It is proposed that, while the N-terminus of the peptide may be embedded in the bilayer in analogy with dynorphin (1-13), the C-terminal region of dynorphin A (1-17) bends back onto the bilayer/water interphase, and that the Trp14 residue is stabilized in a hydrophobic pocked near the interphase by the interaction of the neighboring charged amino acids with the phosphate, carboxyl and amino groups on phosphatidylserine.

Amino Acid Sequence↗
PubMedDate not supplied

Non-uniform triple helical structure in chick skin type I collagen on thermal denaturation: Raman spectroscopic study.

The individual chains in the triple helix of collagen occur in a conformation related to polyproline II because of the presence of large number of imino peptide bonds. However, these residues are not evenly distributed in the collagen molecule which also contains many non-imino residues. These non-imino regions of collagen may be expected to show preference for other than triple helical conformations. The appearance of several Raman bands in solution phase at 65 degrees C raises the possibility of non-uniform triple helical structure in collagen. Raman spectroscopic studies on collagen in the solid state and in solution at a temperature greater than its denaturation temperature, reported here suggest that denatured collagen may exhibit an ensemble of conformational states with yet unknown implications to the biochemical interactions of this important protein component of connective tissues.

Animals↗