Interaction of β-Aminoethylisothiouronium Bromide Hydrobromide with the Bases of DNA, Basic Amino-Acids and Nucleohistone

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.