Asp Gly Research Articles

The Role of Lys Side Chains in the Stabilization of β-Turn Structure

Peptides containing Lys and Orn were synthesized to study the role of side chains in the formation of the β-turn structure. In contrast with peptides having a –Lys–Asp– sequence, peptides containing an –Orn–Asp– sequence do not adopt a β-turn structure. Analysis of the side chain rotamers shows that in Boc–Gly–Lys–Asp–Gly–OMe the Lys side chain can interact with the side chain of the neighboring Asp residue and this interaction contributes to the stabilization of the β-turn structure. The Orn side chain, instead of side chain–side chain interactions, interacts with the peptide backbone.

Fractionation of the multiple forms of bovine gastric aspartic proteases by chromatofocusing

By extending the chromatofocusing technique to a very acidic pH range (down to pH 2.0) a method which, in a single-step procedure, allows separation of the three main aspartic proteases secreted by the bovine abomasal mucosa i.e., chymosin (EC 3.4.23.4), gastricsin (EC 3.4.23.3), and pepsin A (EC 3.4.23.1), has been developed. Starting materials for separation were crude commercial milk-clotting extracts or abomasal juices. A multistep procedure, using narrower pH gradients, enabled the fractionation of these proteases into their multiple forms. Chymosins A and B, which are known to differ only by a single amino acid substitution ( Asp Gly ), were completely resolved. Their elution pHs, 3.75 and 3.80, respectively, though far from their “normal” p Is (around 4.7 in isoelectric focusing), demonstrate the resolving power of such a technique. Multiple forms of bovine pepsin A, which differ in their organic phosphate content (0–3 phosphate group(s) per molecule of enzyme) and whose p Is are lower than 2.5 were also separated using 15–20 m m glycine buffer, pH 2.0, as eluent. Although many attempts to get a linear gradient remained unsuccessful within this pH range, resolution appeared quite satisfactory, as judged from analytical isoelectric focusing patterns. In particular, the two subcomponents of bpA 1, which presumably have a different site of post-translational phosphorylation, were resolved in this way.

Structure-taste Relationships of Aspartyl Tripeptide Esters

Abstract A series of twenty four analogues of l-α–Asp–Gly–Gly–OMe has been synthesized in relation to structural features of sweet peptides. The rule in the structure-taste relationships of dipeptides is held in the sweet aspartyl tripeptide esters. In order for the aspartyl tripeptide esters to be sweet, the second amino acid must have a d-configuration and a small, compact alkyl group (Me, Et, or i-Pr) at R2. An l-configuration of the third amino acid is required for a potent sweet taste. It has been concluded that the small alkyl group at R2 participates in binding with the receptor through a hydrophobic interaction and increases the sweetness potency.