β-Asp1, Val5-Hypertensin II, ein Hypertensin-Analoges besonders hoher biologischer Aktivität

Role of the two N-terminal residues of angiotensin II in the production of tachyphylaxis

The structural requirements for the production of angiotensin tachyphylaxis in the guinea-pig ileum were studied by analyzing the tachyphylactic properties of the following synthetic analogues of angiotensin II (AII): [1-sarcosine]AII, [1-betaine]AII; [1-guanidinoacetic]AII; betainyl-AII; [2-lysine]AII; [2-ornithine]AII. In the non-atropinized ileum, no tachyphylaxis was observed with any of the following analogues: [2-lysine]AII, [2-ornithine]AII, [2-ornithine]AII, [1-betaine]AII and betainyl-AII. [1-Guanidinoacetic]AII induced tachyphylaxis, but to a smaller degree than AII, while [1-sarcosine]AII was significantly more tachyphylactic than AII. Similar results were obtained in the atropinized ileum, except that moderate tachyphylaxis was also observed with betainyl-AII and [1-betaine]AII. The analogues with lysine or ornithine residues in position 2 did not induce tachyphylaxis under any of the conditions studied. It is concluded that, besides the protonated N-terminal amino group, the guanidino group of the Arg2 side-chain is essential for the manifestation of angiotensin tachyphylaxis in the guinea-pig ileum.

Mechanisms of heat damage in proteins. 2. Chemical changes in pure proteins

1. Bovine plasma albumin (BPA) containing approximately 14% moisture, when heated for 27 h at 115° suffered an appreciable loss of cystine and a small loss of lysine; at 145° all the amino acids except glutamic acid and those with paraffin side-chains, showed considerable losses. Isoleucine also showed some loss through racemization to alloisoleucine.

2. BPA heated at 115° evolved H2S; at 145° other sulphur compounds were released as well, all coming from the breakdown of cystine. Possible mechanisms for this are discussed.

3. Ammonia was also liberated from BPA heated at 115°. The degree of correlation of lysine binding in different proteins with ammonia liberation and amide changes has led us to suggest that the main reaction of ε-amino lysine groups is with amide groups of asparagine and glutamine. Reaction of ε-amino groups with carboxylic groups is thought to be less important.

4. Model experiments have shown that a reaction between amide groups and the e-amino group of lysine in proteins can occur at practical drying temperatures.

5. Reactions of the ε-amino group of lysine with destruction products of cystine is also considered to be partially responsible for the lysine binding in heated proteins.