Frequency and Markov chain analysis of the amino-acid sequence of human alcohol dehydrogenase alpha-chain.

The amino-acid sequences of human alcohol dehydrogenase alpha-chain (ADH1) were analysed according to two-, three- and four-amino-acid sequences. The measured frequencies and probabilities were compared with the predicted frequencies and probabilities. Of 373 two-amino-acid sequences in the ADH1, 92 (24.665%) and 32 (8.579%) sequences can be explained by the predicted frequencies and probabilities according to a purely random mechanism. Of 191 non-appearing two-amino-acid sequences in the ADH1, 119 (62.304%) and 52 (27.225%) sequences can be explained by the predicted frequencies and probabilities according to a purely random mechanism. Of 373 measured first-order Markov transition probabilities for the second amino acid in two-amino-acid sequences, three (0.804%) probabilities match the predicted conditional probabilities and therefore can be explained by a purely random mechanism. No more-than-two-amino-acid sequences can be explained by a purely random mechanism.