Starvation induced cholesterogenesis in hepatic and extra hepatic tissues of climbing Perch, Anabas testudineus (Bloch).

Cholesterol is a structural lipid, which may be differentially utilized or synthesized in response to stress or during insulin deficient states such as starvation. In the present investigation we estimated the levels of cholesterol in Anabas testudineus, which was subjected to brief (15 days) and prolonged fasting (60 days). Tissues such as liver, kidney, brain, accessory respiratory organ, pectoral and lateral line muscle were selected for the study. Cholesterol content was estimated by the Crawford method (1958). Both the starvation regimes showed a significant increase in cholesterol levels in almost all the tissues, but for liver, which strangely showed an insignificant decline during the short-term starvation. This overall upsurge in cholesterol levels observed in all extra hepatic tissues may be attributed to the synthesis of stress hormones such as glucocorticoids, which may promote gluconeogenesis and adrenocorticoids, which may help the animal to combat the stressful condition of starvation. Anabas adapted well to starvation stress and survived all throughout the experimental period.

Cyclic homooligomers of furanoid sugar amino acids.

Cyclic homooligomers of mannose-derived furanoid sugar amino acid 1 [H-Maa(Bn(2))-OH] were synthesized by using BOP reagent in the presence of DIPEA under dilute conditions that converted the sugar amino acid monomer directly into its cyclic homooligomers 3a and 4a. The glucose-based sugar amino acid 2 [H-Gaa(Bn(2))-OH] under the same reaction conditions gave a bicyclic lactam 5a as the major product. Cyclic homooligomers of 2 were prepared by cyclizing their linear precursors 6 and 7 leading to the formation of cyclic peptides 8a and 9a, respectively. Conformational analysis by NMR and constrained MD studies revealed that all the cyclic products, 3, 4, 8, and 9, had symmetrical structures. The deprotected cyclic trimer of Maa 3b displayed a conformation in which all the C=O and the N-H bonds of the molecule point in opposite directions. In the deprotected cyclic tetramer of Maa 4b, the COs and NHs were in the plane of the ring with the former pointing to outside and the latter inside the ring. The structure of the cyclic Gaa dimer 8b displayed an unusual six-membered intramolecular hydrogen bond between NH(i)() --> C3-O(i)()(-)(1) and a syn orientation between the C2-H and CO. In this molecule, the C2-hydrogens and the COs can be seen on one side of the ring while the NHs point to the other side. Addition of the bicyclic lactam 5b resulted in the influx of Na(+) ions across the lipid bilayer leading to the dissipation of valinomycin-mediated K(+) diffusion potential.

Antibacterial and hemolytic activities of single tryptophan analogs of indolicidin.

The structure and biological activities of analogs of the bovine neutrophil antibacterial and hemolytic peptide indolicidin, ILPWKWPWWPWRR-amide, where one tryptophan at 4th, 8th, or 11th position has been retained and the others replaced by leucine, have been investigated. All the single tryptophan analogs exhibit antibacterial activity. However, unlike indolicidin, they do not lyse erythrocytes. Structure analysis by circular dichroism spectroscopy indicates that the analogs are unordered in aqueous medium and adopt beta-turn structures in trifluoroethanol and micelles. The tryptophan residues in indolicidin appear to be essential for hemolytic activity but not antibacterial activity. The nonspecific biological activities of indolicidin and specific antibacterial activity of single tryptophan analogs suggest that in short peptides, a motif composed of hydrophobic amino acids with the exception of tryptophan, interspaced with proline residues and cationic amino acids at the N or C termini would favor selective antibacterial activity.

Norbornene-constrained cyclic peptides with hairpin architecture: design, synthesis, conformation, and membrane ion transport.

A novel family of hairpin cyclic peptides has been designed on the basis of the use of norbornene units as the bridging ligands. The design is flexible with respect to the choice of an amino acid, the ring size, and the nature of the second bridging ligand as illustrated here with the preparation of a large number of norborneno cyclic peptides containing a variety of amino acids in ring sizes varying from 12- to 29-membered, with the choice of the second bridging ligand being a rigid norbornene (11, 13a,b), an adamantane unit (7a,b and 8), or a flexible cystine residue (4a,b and 10). The presence of built-in handles (as protected COOH groups) permits the attachment of a variety of subunits as shown here with the ligation of Leu-Leu, Val-Val, or Aib-Aib pendants in 4b, 7b, and 13b, respectively. This novel class of constrained cyclic peptides are demonstrated to adopt beta-sheet- or hairpin-like conformation as shown by (1)H NMR and CD spectra. Membrane ion-transport studies have shown that the norborneno cyclic peptides 4b and 7b containing Leu-Leu or Val-Val pendants symmetrically placed on the exterior of the ring show high efficiency and selectivity in the transport of specifically monovalent cations. This property can be attributed to the hairpin-like architecture induced by the norbornene unit since the bis-adamantano peptide 15 containing two pairs of Leu-Leu pendants on the exterior is able to transport both monovalent (Na(+), K(+)) and divalent (Mg(2+)/Ca(2+)) cations.

Addition and omission analogs of the 13-residue antibacterial and hemolytic peptide PKLLKTFLSKWIG: structural preferences, model membrane binding and biological activities.

The consequences of selective addition or deletion of polar amino acids in a 13-residue antibacterial peptide PKLLKTFLSKWIG on structure, membrane binding and biological activities have been investigated. The variants generated are (a) S and T residues replaced by K, (b) S and T residues deleted individually and together, (c) introduction of two additional K and (d) deletion of L and L with T. In the aqueous environment all the peptides were unordered. In trifluoroethanol, the spectra of peptides belonging to groups (a-c) suggest distorted helical conformation. Peptides in group (d) appear to adopt beta-sheet conformation. The peptides bind to zwitterionic and negatively charged lipid vesicles, although to different extents. With the exception of peptides in group (d), all the other peptides exhibited comparable antibacterial activity against Escherichia coli and Staphylococcus aureus. However, the changes made in the peptides in groups (a-c) resulted in reduction of hemolytic activity compared to the parent peptide. Extent of binding to lipid vesicles composed of phosphatidylcholine and cholesterol appears to correlate with hemolytic activity. It appears that polar and charged residues play a major role in modulating the biological activities of the 13-residue peptide PKLLKTFLSKWIG. The 11-residue peptide-like PKLLKFLKWIG has selective antibacterial activity. Thus, by judicious engineering it should be possible to generate short peptides with selective antibacterial activity.