Distributions of amino acid residues in proteins show that proline is overrepresented in sequence positions following two basic residues (${LysArg}−{LysArg}$), i.e. at sites similar to those susceptible to proteolytic cleavages of hormonal pro-forms. Conformational correlations further show that ${LysArg}−{LysArg}$-Pro sequences are often (8/11) not adiacent to elements of secondary structure, whereas the opposite applies to ${LysArg}−{LysArg}$-nonPro sequences (82/103 adjacent to elements of secondary structure). These distribution patterns from proteins in general also seem applicable in individual protein groups as demonstrated for some dehydrogenases. It appears possible that ${LysArg}−{LysArg}$-nonPro constitutes a restricted sequence, n proteins, and that proline, in addition to elements of secondary structure, contributes a means of avoiding unacceptable proteolytic processings of proteins in general.

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