use strict;

my $string = "DEFINITION  BIO5 gene complete cds EC=1.7.7.1.
ACCESSION   D17396
VERSION     D17396.1  GI:498167
KEYWORDS    protein; insulin-like protein;";

my %KVpairs = ($string =~ /(\w+)\s+(.*)/mg);#save the result right into a hash
foreach (keys %KVpairs) {
   print "[$_] = $KVpairs{$_}\n";
}