NISCAIR Online Periodicals Repository Community: IJBB Vol.38 [2001]

Conformational study of peptides containing dehydrophenylalanine Helical structures without hydrogen bond

Wed, 28 Nov 2001 22:58:59 GMT

Title: Conformational study of peptides containing dehydrophenylalanine Helical structures without hydrogen bond

Authors: Nandel, Fateh S; Kaur, Harpreet; Malik, Nandita; Shankar, Neelaabh; Jain, Dharam V S

Abstract: The conformational behaviour of ∆^zPhe has been investigated in the model dipeptide Ac-∆^z Phe-NHMe and in the model tripeptides Ac-X-∆^z Phe-NHMe with X=Gly, Ala,Val, Leu, Abu, Aib and Phe and is found to be quite different. In the model tripeptides with X=Ala, Val, Leu, Abu, Phe the most stable structure corresponds to ₁=-30°, ψ₁= 120° and ₂₌ψ₂ =30°. This structure is stabilized by the hydrogen bond formation between C=O of acetyl group and the NH of the amide group, resulting in the formation of a 10-membered ring but not a 3₁₀ helical structure. In the peptides Ac- Aib-∆^z Phe-NHMe and Ac-(Aib-∆^z Phe)₃-NHMe, the helical conformers with =±30°, ψ= ±60° for Aib residue and = ψ= ±30° for ∆^z Phe are predicted to be most stable. The computational studies for the positional preferences of ∆^z Phe residue in the peptide containing one ∆^z Phe and nine Ala residues reveal the formation of a 3₁₀ helical structure in all the cases with terminal preferences for ∆^zPhe. The conformational behaviour of Ac-(∆^z Phe)_n-NHM_e with n≤4 is predicted to bc very labile. With n> 4, degenerate conformational states with j, ψ values of 0° ± 90° adopt helical structures which are stabilized by carbonyl-carbonyl interactions and the N-H-π interactions between the amino group of every ∆^z Phe residue with one C-C edge of its own phenyl ring. The results are in agreement with the experimental finding that screw sense of helix for peptides containing ∆^z Phe residues is ambiguous in solution. The helical structures stabilized by hydrogen bond formation are found to be at least 3kCalmol^-1 less stable. Conformational studies have also been carried out for the peptide Ac-(∆^E Phe)₆,-NHMe and the peptide Ac-∆Ala- (∆^z Phe)₆-NHMe containing ∆Ala residue at the N-terminal. The N-H -π interactions are absent in peptide Ac-(∆^E Phe)₆-NHMe.

Page(s): 417-425

Role of liquid membrane phenomenon in biological actions of ACE inhibitors, captopril and lisinopril

Wed, 28 Nov 2001 22:58:59 GMT

Title: Role of liquid membrane phenomenon in biological actions of ACE inhibitors, captopril and lisinopril

Authors: Nagappa, AN; Patil, R T; Pandi, V; Ziauddin, K

Abstract: The liquid membrane phenomenon in angiotensin convening enzyme (ACE) inhibitors namely, captopril and lisinopril has been studied. Hydraulic permeability data have been obtained 10 demonstrate the existence of the liquid membrane in series with a supporting membrane generated by the ACE inhibitors. Data on the transport of the relevant permeants in presence of the liquid membrane formed by ACE inhibitors indicate that liquid membrane phenomenon is likely to playa significant role in the action of ACE inhibitors.

Page(s): 412-416

Effect of γ-irradiation on H3 histone and DNA in solution

Wed, 28 Nov 2001 22:58:59 GMT

Title: Effect of γ-irradiation on H3 histone and DNA in solution

Authors: Upadhyay, S N

Abstract: Three methods, namely, absorbance of colour by reaction with Folin-Ciocalteau reagent, UV absorbance and fluorescence intensity measurements for detection of H3 histone in 0.15 M standard saline citrate (SSC) solution were compared. Maximum sensitivity was found with the Folin-Ciocalteau method. Effect of varying pH and of γ - radiation on H3 hi stone and on interaction of H3 hi stone with DNA were studied. For this, solutions of H3 histone in SSe. in 0.9% NaCl, H3 hi stone + DNA in 0.9% NaCI were subjected to varying pH (1-10) and γ - radiation (dose 10-50 Gy) and λ_max and A_λmax),max were monitored. From the molar ratios of histone and DNA in the complex, it was observed that at γ-radiation dose of 50 Gy and pH 8.54, there was a depletion of 6-8 μg/ml of histone from the histone-DNA complex .

Page(s): 406-411

Effect of a water soluble derivative of α-tocopherol on radiation response of Saccharomyces cerevisiae

Wed, 28 Nov 2001 22:58:59 GMT

Title: Effect of a water soluble derivative of α-tocopherol on radiation response of Saccharomyces cerevisiae

Authors: Singh, Rakesh K; Verma, Naresh C; Kagiya, V T

Abstract: The radioprotection conferred by a highly water soluble glucose derivative of α -tocopherol, namely, 2-( α-D-glucopyranosyl) methyl-2.5,7,8-tetramethylchroman-6-ol (TMG) in Saccharomyces cerevisiae was studied. Cells grown in standard YEPD-agar medium and irradiated in the presence of TMG showed a concentration dependent higher survival up to 10 mM of TMG in comparison to cells irradiated in distilled water. Treatment of TMG to cells given either before or immediately after irradiation but not during irradiation, had no effect on their radiation response. S.cerevisiae strain LP1383 (rad52) which is defective in recombination repair showed enhanced radioresistance only when subjected to irradiation in presence of TMG. Cells of radS2 strain grown in the medium containing TMG showed a radiation response similar to that of cells grown in the medium without TMG. The nature of TMG dependent enhanced radioresistance was studied by scoring the mutations in the strain D-7, which behaved like wild type strain in complete medium, at trp and ilv loci . Our study indicated that TMG confers radioresistance in S. cerevisiae possibly by two mechanisms viz. (i), by eliminating radiation induced reactive free radicals when the irradiation is carried out in the presence of TMG and (ii ), by activating an error - prone repair process involving RAD52 gene, when the cells are grown in the medium containing TMG.

Page(s): 399-405