$desc =~ /.+\[(.+)\]\s*$ (?{ $org = $1 or ''; })/x;

##</code><code>##

my $enz, my $org;
my $rx_enz_org = qr/
  (.+)\[(.+)\]\s*$ 
  (?{ 
    $enx = $1 or '';
    $org = $2 or ''; 
  })
/x;
<begin $desc loop>
  $desc =~ /$rx_enz_org/;
<end loop>