Table 1. Rate constants for repair of DNA guanyl radicals by amino acids and their methyl or ethyl esters.

Parent amino acid	k5 (dm3 mol–1 s–1)
	Free acid	Methyl or ethyl estera	N-acetyl amide
Cysteine	2.0 × 106	8.8 × 105	2.7 × 105
Cystine	3.4 × 105	<2.0 × 104
Histidine	<2.0 × 104	<2.0 × 104
Methionine	7.7 × 105	8.3 × 104	<2.0 × 104
Tryptophan	4.4 × 107	1.0 × 107	7.7 × 106
Tyrosine	1.7 × 106	4.0 × 105	1.9 × 107

^aMethyl ester in all cases except cystine, which was the diethyl ester.