a) Define the terms Km, kcat and kcat/Km and explain briefly what information each provides about an enzyme catalyzed reaction.

b) Rank the five different peptide substrates from table 1 in order of best to worst substrate for ACE. Explain very briefly how you have determined the order

Problem 2: Angiotensin Converting Enzyme (ACE) [8 marks] Angiotensin Converting Enzyme (ACE) plays an important role in controlling blood pressure because ACE catalyzes the hydrolysis of the decapeptide angiotensin I to the active octapeptide angiotensin II and a dipeptide (His-Leu). In an effort to investigate how important the angiotensin I peptide sequence is to its ability to be a good substrate for the angiotensin converting enzyme (ACE), a series of peptide analogues of angiotensin I (named Angiotensin Ia-d) are created and tested as substrates for ACE. The analogues were created by changing the nature of the amino acid on either side of the peptide hydrolysis site. Table 1 Kinetic parameters of Angiotensin Converting Enzyme