| Popis: |
The recent wide interest in the study of synthetic homoor hetero-polypeptides containing the basic amino acids lysine or arginine clearly originates from two experimental advantages: the good solubility of these polymers or copolymers in aqueous media and their affinity towards polynucleotides, which is caused by strong electrostatic interactions. This has led to investigations of their conformation in aqueous solutions and their interaction with DNA. For inherent reasons, these synthetic polypeptides are mixtures of varying chain length, which is a consequence of the low molecular weight. This is of particular importance for the sequential copolymers whose molecular weights often cannot be raised to high enough levels because of preparative difficulties (Refs 1 and 2 and citations therein). These, and more general, reasons stimulated several investigations into the dependence of the properties of basic oligopeptides on chain length. There are reports on lysine 3"4, ornithine 5 and, recently, on peptides of arginine 6. This paper deals with a continuous series of (Lys-PheLys), oligopeptides, with n values from 3 to 9. The synthesis in our laboratory of sequential lysine and phenylalanine-containing copolypeptides t was extended to include a series of sequential oligopeptides of the type (Lys-Phe-Lys),. A low molecular weight fraction obtained by polymerization of the tripeptide Lys-Phe-Lys was separated on Sephadex CM 25 in 0.5 M sodium acetate by applying a NaCI gradient of 0.4 1.8 M. Of the seven fractions obtained (fractions 3 to 7 were rechromatographed on the same column) only fraction 7 may contain minor portions of the adjacent higher molecular weight oligopeptide. The samples were desalted on Bio-Gel P2 in 0.5 M acetic acid and lyophilized. The degree of polymerization was determined by Edman degradation in a model 12 sequenator from Sequenat Inc., Watertown, USA, after fixation of the peptide on phenylene diisothiocyanate glass beads. The first fraction was found to release phenylalanine in three steps. Consequently, n equals 3, and the subsequent fractions were assumed to have values of n from 4 to 9. |
