http://nopr.niscpr.res.in/handle/123456789/3691 2026-10-05T22:16:41Z http://nopr.niscpr.res.in/handle/123456789/30399 Title: Disruption of distal interactions of Arg 262 and of substrate binding to Ser 52 affect catalysis of sheep liver cytosolic serine hydroxymethyltransferase Authors: Jala, Venkatakrishna Rao; Ambili, M; Prakash, V; Rao, N Appaji; Savithri, H S Abstract: <span style="mso-bidi-language:HI">The crystal structure of human liver cytosolic recombinant serine hydroxymethyltransferase (hcSHMT) suggested that Ser53 and Arg 263 could participate in the reaction catalyzed by SHMT. The mutation of Arg262 (corresponding to Arg263 in hcSHMT) to 'A' in sheep liver cytosolic SHMT (scSHMT) resulted in a 5-fold increase in <i>K</i>_m<i> </i>for L-Ser and a 5-fold decrease <span style="mso-bidi-language:HI">in <i>k</i>_cat<i> </i>compared to scSHMT. Further, in R262A SHMT-glycine complex, the peak at 343 nm (geminal diamine) was more pronounced, compared to wild-type enzyme. Stopped-flow studies showed that the rate constant for the formation of glycine-geminal diamine for R262A SHMT was also decreased. The rate of reaction, concentration of spectral intermediates, fluorescence excitation maximum of glycine geminal diamine and interaction with methoxyamine were altered in R262A SHMT. Although Arg263 in hcSHMT is located outside the PLP binding pocket, it positions Tyr73 for interaction with PLP, by forked H-bonding with the carbonyl groups of main chain residues, Asn71 and Lys72 of the other subunit of the tight dimer. Mutation of Arg262 to Ala and the consequent alteration in orientation of PLP leads to decreased catalytic efficiency. Ser53 (in hcSHMT) is in hydrogen bonding distance to one of the carboxylate oxygens of the amino acid substrate, which also interacts with Tyr83 and Arg402. Replacement of Ser53 with Cys (using <span style="mso-bidi-font-family:Arial;mso-bidi-language:HI">'O' <span style="mso-bidi-language:HI">software program) in the structure of hcSHMT resulted in disruption of these interactions, whereas replacement with Ala (S53A) only weakened the substrate interactions. There was a 10-fold increase in <i>K</i>_m<i> </i>and 20-fold decrease in catalytic activity efficiency for S52C <span style="mso-bidi-language:HI">SHMT, whereas S52A SHMT retained 20% of the activity without change in <i>K</i>_m<i> </i>for serine. These results suggest that S52 affects substrate binding and catalysis. </span></span></span></span></span> Page(s): 226-237 2003-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/3803 Title: Beneficial effects of tender coconut water against isoproterenol induced toxicity on heart mitochondrial activities in rats Authors: Anurag, P; Rajamohan, T Abstract: Myocardial infarction induced by isoproterenol results in increased mitochondrial lipid peroxidation, decreased activities of carnitine acetyl transferase, acyl CoA dehydrogenase, TCA cycle enzymes and decreased rate of palmitate oxidation into CO₂ and ATP formation in the heart in rats. Isoproterenol-induced rats when fed with tender coconut water (West coast tall variety, 5-6 months age) showed improved activities of these mitochondrial enzymes and higher rate of palmitate oxidation into CO₂ and ATP production. These results indicate that intake of TCW has a significant beneficial effect on mitochondrial activities. Page(s): 278-280 2003-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/3802 Title: Purification and partial characterization of cytochrome c₅₅₂ from Halobacterium salinarium Authors: Sreeramulu, K Abstract: Cytochrome c₅₅₂ was purified to near homogenity and partially characterized from Halobacterium salinarium JWS mutant, devoid of carotenoid pigments. The purification involved the extraction of membranes with 1% Triton X-100, followed by butylagarose, DEAE-Sepharose CL6B and hydroxyapatite column chromatography. The fold of purification was 16. The purified cytochrome showed maximum absorption at 552 nm. The molecular mass determined by SDS-PAGE was found to be 14.1 kD. Page(s): 274-277 2003-08-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/3801 Title: Effect of terminal achiral and chiral residues on the conformational behaviour of poly Δ^ZPhe and analysis of various interactions Authors: Nandel, Fateh S; Kaur, Harpreet Abstract: Conformational properties of the peptides containing (Δ^ZPhe)6 with achiral (ΔAla, Gly) and chiral (Ala, Leu) residues at both the N- and C-terminal positions have been studied with a view to design a peptide with desired helical screw sense. In all the peptides, the lowest energy conformational state corresponds to φ = 0º and Ψ = + 90ºor – 90º or both ± 90º. These structures are characterized by rise per residue of 1.94 Å; rotation per residue of 114º and 3.12 residues per turn and are stabilized by: (i) carbonyl-carbonyl interactions with the carbonyl oxygen of ith residue and carbonyl carbon atom of the carbonyl group of ith+1 residue; and (ii) N-H…π interactions between the amino group of Δ^ZPhe and its own aromatic moiety. The Ala/Leu residues at the N-terminus further stabilized the structure, through C-H…π interactions with the farthest edge of the aromatic ring of ith+3 Δ^ZPhe residue. For peptides Ac-L-Ala/L-Leu-(Δ^ZPhe)6-NHMe, the low energy left handed helical structure (~2.5 Kcalmol-1 higher in energy) state corresponds to φ = -30º, Ψ = 120º for L-residue and φ = Ψ = 30º for Δ^ZPhe residues and is in good agreement with the X-ray crystallography results for the peptide Boc-L-Ala-(Δ^ZPhe)4-NHMe crystals grown from acetonitrile/ethanol mixture. Computational results suggest that the peptides Ac-D-Ala/D-Leu-(Δ^ZPhe)6-NHMe adopt a right handed helical structure in polar solvents with φ = 30º, Ψ = -120º for D-residues and φ = Ψ = -30º for Δ^ZPhe residues. Both in the left handed and right handed structures, the carbonyl oxygen of acetyl group is involved in 10-membered hydrogen bonded ring formation with NH of 3rd Δ^ZPhe residue whereas Δ^ZPheresidues backbone adopts a 3₁₀ helix structure. Computational results also suggest that the conformational state with φ = 0º and Ψ = 90º can be realized by keeping D-Ala or D-Leu at the C-terminal. There is hardly any effect of achiral residues Gly/ΔAla on the conformational behaviour of poly-Δ^ZPhe. Page(s): 265-273 2003-08-01T00:00:00Z