Differential sequence environment of oxidation-resistant and oxidation-prone methionines.
The frequencies of amino acids flanking each oxidized methionine were recorded. This operation was repeated to compute the frequencies around non-oxidized methionine residues. The differences between these two frequency sets were used to determine the standard score, Zij, according to the equation 1 from the text, where i indicates the amino acid whose frequency is being analysed and j is the position around the central methionine at which the frequency is being computed. A standard score that is much greater than zero or much less than zero indicates that amino acid i is overrepresented or underrepresented at position j, respectively, in an environment of oxidation-prone methionines with respect to an environment of oxidation-resistant methionines. The bar chart (upper left corner) represents the sum of the absolute values of the standard score for each amino acid, considering the 20 positions around the central methionine (. At each position, the standard scores for the seven amino acids contributing more strongly to a differential environment (Y, M, W, H, E, R and K) were plotted.