80 UNITY AND DIVERSITY IN BIOCHEMISTRY 



The tyrocidines are antibiotic peptides produced at the same time as the 

 gramicidines. Among their amino acids are L-ornithine and D-phenylalan- 

 ine. The penicilUns, produced by moulds of the genus Penicillium, are 

 derived from a dipeptide, a-formylglycyl-D-penicillamine. 



CH3 CH3 CH3 



\ / I 



C— SH CHO H3C— C— SH 



HoN— CH— COOH H2N— CH— CO NH— CH— COOH 



Penicillamine a-formylglycyl-D-penicillamine 



In penicillin G, for example, the penicillamine is cyclized into a thiazo- 

 lidine ring by reaction of the aldehyde group (formyl radical) with the 

 thiol and NH groups. 



CHo -CO-NH CH CH C^ 



I I I 



OC N CH 



CHa 



COOH 



Penicillin G 



In Other penicillins the benzene ring of penicillin G is replaced by other 

 groups. 



(c) Phalloidin 



The poison present in the fungus most commonly responsible for cases 

 of poisoning, Amanita phalloides, is a peptide known as phalloidin. On 

 hydrolysis, it gives cystine and alanine, but, in addition, allohydroxy-L- 

 proline, a diastereoisomer of the form of proline found in proteins. 



{d) Peptide Hormones 



The peptide type of structure is frequently employed for the chemical 

 transmission of messages by means of hormones. An example is provided 

 by the two hormones of the posterior hypophysis of vertebrates, oxytocin 

 and vasopressin. These two polypeptides have been extracted from the 

 gland itself, by rather a drastic treatment such that it still remains debatable 



