Convergent evolution in chemotrypsin and subtilisin

[Gary S. McKenzie]

Hi
Can someone inform me of recent refs in regards to the above specifically 
in regards to the convergent evolution of the catalytic triad that is 
similar in both mammals and bacterial species. Why should the vertebrate 
pancreatic serine proteases and bacterial subtilisin have attained the 
same solution by independent parallel evolutionary processes??
Thanx
G. Mckenzie
cegsm at blaze.TrentU.Ca