International Journal of Protein Research 

About: International Journal of Protein Research is an academic journal. The journal publishes majorly in the area(s): Amino acid & Peptide. Over the lifetime, 107 publications have been published receiving 1938 citations.

Study of hydrogen bonds in amino acids and peptides.

Abstract: An analysis of the various parameters associated with N-H… O type of hydrogen bonds has been made using data from reported crystal structures of amino acids and simple peptides. The different parameters at the donor and the acceptor ends have been suitably defined and evaluated. In some cases the analysis is done depending upon the chargedness or other characteristics of the donor and acceptor groups. Histograms giving the distribution of these parameters have been drawn and possible conclusions arrived at: 1. The distribution shows a maximum between 2.8 A and 2.9 A for the charged donor group and 2.9 A and 3.0 A for the uncharged donor group and is probably not dependent upon the charge on the acceptor group. 2. The angle between the directions CO and O. N tends to lie between two cones about C O with semi-vertical angles 40 and 70°. The orientation of the directions O. N and O. H with respect to the lone pair orbital directions on the acceptor oxygen atoms are analysed in detail using spherical polar coordinates. The analysis indicates that the group NH has a very strong tendency to point towards the acceptor oxygen atom. A general feature has been found in that the direction N-H tends to be closer to an orbital if the oxygen is an acceptor of two hydrogen bonds, while the direction tends to lie in between the orbitals when the acceptor oxygen is the receipient of only one hydrogen bond. The possible explanation of this on the basis of lone pair interaction is briefly discussed.

Thermophilic aminopeptidases from bacillus stearothermophilus. i. isolation, specificity, and general properties of the thermostable aminopeptidase i *

Abstract: A thermostable aminopeptidase (AP 1) from homogenates of B. stearothermo-philus was purified by filtration on Sephadex G-150, by heat treatment, by chromatography on DEAE Sephadex and Sephadex G-200, and by preparative polyacrylamide gel electrophoresis. The enzyme shows one band in polyacrylamide gel electrophoresis and has a pH optimum between 7.5 and 8 for LNA and between 9.2 and 9.4 for Gly-Leu-Tyr. One striking feature in the amino-acid composition of AP I in comparison with the data of leucinaminopeptidase is the larger proportion of hydrophobic amino-acid residues and of glycine. As regards its specificity, AP I differs from other amino-peptidases in certain important respects. The activation energy for the hydrolysis of Leu-Gly was calculated to be 16,300 cal/M-1. The enzyme remains stable for several hours at 80 C; after 30 min at this temperature the activity increases by about 20 per cent (Vm increases, while Km remains the same). The stability of the enzyme in urea, dodecyl sulphate, and various alcohols was studied. The activity of the enzyme even increases in 10 per cent tertiary butanol, in the same way as after heat treatment (Vm increases, while Km remains the same). The kinetics of the increase in activity following heat treatment or in 10 per cent tertiary butanol are discussed. At 20°C, AP I exhibits a sigmoidal dependence of reaction velocity on the concentration of LNA whereas at 40°C or 80°C the curves show a hyperbolic behaviour. In the metal-enzyme complex of AP I the Co2+ ions are strongly bound at pH 8 (up to 10-2MEDTA). At a pH lower than 6 the stable apo-enzyme is formed in 10-2M EDTA. The apo-enzyme can be reactivated to the holo-enzyme by adding Co-2. The metal-enzyme complexes of various metals show different substrate specificities.

Studies on the conformation of amino acids. VI. Conformation of the proline ring as observed in crystal structures of amino acids and peptides.

Abstract: The paper deals with an analysis of the available crystal structure data related to proline compounds so as to obtain information about bond lengths, bond angles, and the conformation of the pyrrolidine ring. The interesting results are: 1. The atoms Cβ, Cα, N, and Cs are nearly coplanar, with the torsion angle 0 about the Cα - N bond varying from about -15° to -15°. The Cγ atom is displaced from this plane, either up or down, so that the ring exists in one of the two puckered conformations, designated A and B. Conformation A is characterized by negative and may be termed Cγ-exo when referred to the displacement of the carbonyl carbon C. Conformation B has positive x l and is Cγ-endo; Cγ-exo is slightly preferred over C-endo, although both conformations occur simultaneously in some crystal structures with partial probabilities. In the other structures, the non-occurring position for C y is found to be disallowed by intermolecular contacts. The proline conformations observed correspond to the 'envelope' type of conformation of the cyclopentane ring. In peptides, the three bonds at N are nearly coplanar, and the torsion about N- Cα bond is nearly - 60°. 2. The observed ranges of (x 1 , x 2 , x 3 , x 4 ) are (0 to –30°, 15 to 50°, –15 to - -30°, 5 to 25°) for conformation A and (20 to 35 0 , -30 to - 40 0 , 20 to 35°, 5 to -20°) for conformation B; for θ and φ the ranges are -15° to -15°, -45 to -75°. The bond lengths and bond angles are not influenced by the conformation of the ring, unlike ribose.