Journal of Surface Science and Technology

S. N. Upadhyay ¹, Rampal Singh ¹, A. K. Gupta ¹, A. Ghose ¹

Affiliations
1 Radiation Biology Division, Institute of Nuclear Medicine and Allied Sciences, Lucknow Road, Delhi 110007, IN

Abstract

The absorption value for reconstituted DNH is less than that of DNA in the X-peak in the unirradiated state. For Y-peak, intensity of absorption is lower for DNA and those for H₃-histone and reconstituted DNH am same. With increasing pH, hyperchromicity of H₃-histone slowly increases indicating unfolding of peptide bonds with increasing pH. Consideration of Y/X ratio reveals that the degree of denaturation by gamma irradiation has been more for DNA as compared to reconstituted DNH for the same irradiation dose. Thus protection of DNA against radiation has been noted due to presence of H₃-histone. Denaturation with radiation has been found to be more for DNH reconstituted after irradiation as compared to that of DNH reconstituted before irradiation.

Keywords

DNA, Histone, Reconstituted DNH, Gamma Irradiation.

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S. N. Upadhyay ¹, Rampal Singh ¹, A. Ghose ¹

Affiliations
1 Radiation Biology Department, Institute of Nuclear Medicine & Allied Sciences, Lucknow Road, Delhi-110054, IN

Abstract

The binding of 5-hydroxy-L-tryptophan (HT), a radioprotector, with deoxyribonucleic acid (DNA) and deoxyribonucleohistone (DNH) in 2.5 × 10^-4 MEDTA and 0.9% sodium chloride solutions takes place in the concentration ratio of (a) DNA : HT 25μg/ml : 20-25 μg/ml and (b) DNH : HT 25 μg/ml : 20-25 μg/ml. Analytical evidences show that the modes of binding are by (i) electrostatic interaction (ii) ion condensation (iii) staking and (iv) intercalation. The two solvents EDTA and 0.9% sodium chloride affect the degree of dissociation of DNA and DNH to different extent, and hence attachment mode of HT with these bioplaymers is decided by stereospecific accessibility. The functional groups responsible for binding are phenolic OH,(indole), (side chain of HT), phosphate groups and phosphodiester bond for DNA, and CONH group, lysine and arginine and chromophores like: -C=C-C=N and -C=C-C=O for DNH. The method of calculations of the binding has been given.

Keywords

Binding Ratio Protector 5-Hydroxy-L-Tryptophan.

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S. N. Upadhyay ¹

Affiliations
1 Radiation Biology Department, Institute of Nuclear Medicine & Allied Sciences, Lucknow Road, Delhi - 11 0 054, IN

Abstract

Nucleohistone (DNH) was found to bind with β-Aminoethylisothiouroniurn bromide hydrobromide (AET) in 1:1 concentration ratio. Charge neutralisation complexes were formed between AET and four amino-acids in the follwoing concentration ratios : AET : Tyrosine, 1:1; AET : Lysine, 10:1; AET : Histidine 5:1 and AET : Arginine 5:1. Binding of AET with the bases (e.g., AET : Adenine, 1:2; AET : Thymine 1:2; AET : Guanine, 1:4 and AET : Cytosine, 1:1.2) in the concentration ratios indicated were through hydrogen bond. The strengths of the binding were found to be AET-Thymine > AET-Guanine > AET-Cytosine > AET-Adenine. C-S-C bond, alkane groups, =NH and -NH₂ groups of AET were responsible for binding. All the amino-acids were protonated by -SH group of mercaptoethylguanidine (MEG). Phosphate ions of DNA and two chromophoric groups, namely -C=C-C=O and -C=C-C=N- were responsible for binding. Upon gamma irradiation, the side chains (e.g., -NH₂, =NH), C-S-C bond and alkane groups of AET got disrupted with increase in dose. But for DNH, helix to coil transition, dissociation of constituent amino-acids and unfolding of the chromophoric groups took place. AET-amino acid complexes produced alkalinity upon gamma irradiation. A probable radiation protection mechanism offered by MEG for DNH has been provided.

Keywords

AET, DNH, Bases, Amino-Acids, Chromophores, Binding, Radiation Protection.

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S. N. Upadhyay ¹

Affiliations
1 Radiation Biology Department, Institute of Nuclear Medicine & Allied Sciences, Lucknow Road, Delhi 110 054, IN

Abstract

Protamine showed a linear response with concentration so far as absorbance is concerned at 210 nm and 230 nm in the concentration range of 2-20 × 10^-5 g/ml. Isoelectric point of reconstituted DNP has been found to be at pH 3.25. On storage, relative absorbance values for DNP varied inversely with concentration. With storage or heat-denaturation, the relative absorbance values for native and reconstituted DNP were similar. The degree of denaturation for both were maximum for heat-denatured samples, followed by storage. With increasing radiation dose, Y-peak values were found to increase consistently for DNA, Protamine, Native and reconstituted DNP. The relative changes in X-peak were comparatively less for all of them. The -C=C-C=C- chromophores of DNA were released in solution as a function of dose whereas -C=C-C=N- chromophores were less released for the same dose range. The changes in protamine with radiation dose occur due to increased chromophoricities of imidazole, tyrosine, histidine and tryptophan. Y-peak values of reconstituted DNP were more comparable to the native DNP. This is due to the increased contribution from protamine as they remain loosely bound to DNA. X-peak values are comparable for the native and the reconstituted DNP; the changes are occurring in DNA whose concentration remains the same in both the cases.

Keywords

Nucleoprotamine, Heat Denaturation, Chromophores, Radiation Dose.

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