The first, second, third and fourth order Markov chain analysis on the amino-acid sequence of human dopamine β-hydroxylase

The repeated amino-acid sequences in human dopamine β-hydroxylase (DBH) may be indispensable for DBH activity, because such repetitions cannot be simply attributed to random chance. The amino acid sequence of human DBH was analysed according to two-, three-, four- and five-amino-acid sequences and their probabilities in human DBH were calculated. The first, second, third and fourth order Markov chain was used to calculate the transition probability for two-, three-, four- and five-amino-acid sequences. The longest repeated sequence is glycine-isoleucine-leucine-glutamic acid-glutamic acid, which appears twice in DBH. The results suggest that the amino acids with a high Markov transition probability may serve as the potential targets of new drugs, because they are unlikely to change into other amino acids.