#!/usr/bin/perl

# http://perlmonks.org/?node_id=1147731

use strict;
use warnings;

my @new_peptides;

my @proteins=qw(
  DAAAAATTLTTTAMTTTTTTCKMMFRPPPPPGGGGGGGGGGGG 
  ALTAMCMNVWEITYHKGSDVNRRASFAQPPPQPPPPLLAIKPASDASD
  );

for my $protein (@proteins) {
  if ($protein =~ m/[KR](?!P)/) {                     
        $protein =~ s/[KR]\K(?!P)/=/g;
        push @new_peptides, split ('=',$protein);
  }
}

for (@new_peptides) {
  print "The peptide is $_\n";
}
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