Amino acid compositions of proteins and their identities

A critical overview is given on the application of amino acid composition data for the establishment of the protein's identity (amino acids composition vs. protein identity, the AAC‐PI method). Several criteria are used to measure the differences between the amino acid compositions of various proteins. The AAC‐PI method unambigiously identifies proteins which belong to the families with a high phylogenetic conservancy of their sequences. The identification of pure proteins can be accomplished with a relatively high level of confidence. The AAC‐PI method, however, sometimes needs the support of N‐terminal or internal sequencing of proteins since, alone, it cannot distinguish whether the lack of finding a candidate protein in protein data bases is because the investigated amino acid composition corresponds to an unknown protein or its processed form or because it is a sum of at least two protein components, or whether it is due to other experimental errors. The identification of a few new proteins such as “arginine‐rich protein”, macrophage migration inhibitory factor (MIF) and the preformed neurotrophic factor present in the calf brain cytosol is also reported. Copyright © 1995 VCH Verlagsgesellschaft mbH