Evaluation of amino acids for their radioprotective efficacy by analytical techniques

lnstitute of Nuclear Medicine & Alied Sciences, Brig. S. K. Mazumdar Road, Delhi-110 054, India

E-mail: snu@inmas.org Fax: 91-011-23919509

Solid State Physics Laboratory, Lucknow Road, Delhi-110 054, India

Manuscript received 16 December 2002, revised 22 August 2003, accepted 8 September 2003

Under two dose rates of 1.16 Gy/s and 0.008 Gy/s, R_f values of 5-hydroxy-L-tryptophan, L-cysteine and cystamine were determined at physiological pH of 6.4-6.5. 5-Hydroxy-L-tryptophan showed consistent decrease in R_f value with increase in dose but not with dose rate and L-cysteine showed increase in R_f value with dose especially at lower dose rate compared to that at higher dose rate, whereas cystamine showed no change in R_f value with increase in dose as well as change in dose rate.

During gamma irradiation, L-cysteine showed positive and cystamine showed negative test for desulphuration, L-cysteine and 5-hydroxy-L-tryptophan showed positive test for decarboxylation. All the amino acids showed positive test for deamination with radiation dose. This has been quantified as a function of dose. Decarboxylation, deamination and desulphuration from respective amino acids have been confirmed by IR spectroscopy.

Number of ammonia molecules liberated per µ mole for a dose of 100 Gy was in the order of 5-hydroxy-L-tryptophan > L-cysteine > cystamine. The radioprotective efficacy as governed by proton acceptance by -NH₂ groups will be in the same order.

Depletion of -SH, -NH₂ and -COOH depends on total dose, dose rate and bond energies of these functional groups. All these determine radioprotective efficacy of selected amino acids.