Conformational studies of basic poly (α-amino acid)s in reversed micelles

Abstract

The conformation of various basic poly (a-amino acid)s was investigated by CD measurements in aqueous solutions containing bis (2-ethylhexyl)sodium sulfosuccinate (AOT) as well as in the AOT reversed micelles. The addition of AOT into an aqueous solution of poly(L-lysine) induces the conformational transition from coil to ordered structure, followed by aggregation. On the other hand, poly(L-lysine) assumes/~-structure in the reversed micelles at low w0value (w0 = [HzO]/[AOT]). Similarly to poly(Llysine), poly(L-ornithine) takes an ordered structure in the aqueous solution containing AOT and/~-structure in the reversed micelles. In this case; however, these ordered structures are not so stable, compared with that of poly(L-lysine). Poly(L-arginine) undergoes the conformational transition from coil to helix by addition of AOT into the aqueous solution. Further addition of AOT allows transformation into/~-structure. Copoly(Llysyl-L-leucine) with 63 % leucine residue was shown to take a stable helical conformation even in pure water. In the reversed micelles, however, this ordered structure is significantly changed probably because the hydrophobic interaction among the leucyl residues is lowered in the reversed micetles.

Association of poly-(L-lysine) homologues in sodium carbonate solution

“…In the CD band the characteristics of an a-helix were found in 30 % methanol with 0.1 M Na2CO3 at pH The results of the CD measurements of (Orn)n agree very well with the previous results of Chaudhuri and Yang [14]. It is known that (Orn)n has a complete helix structure in a neutral solution with sodium dodecyl sulfate SDS (which is a surface-active agent [14]), and a ~structure only in the reversed micelle solution system with Bis(2-ethylhexyl) sodium sulfosuccinate (AOT) [11]. In the presence of carbonate ions, (Orn)n was given a partial helical structure, but did not form a fl-structure as did (Lys)n. Moreover, when this solution was heated to 50 ~ the CD band did not vary, and a white and cloudy precipitate did not appear.…”

“…The general formula of these polymers, *) This paper was presented at the "VI. Symposium on Analytical Ultrace~trifugation', Marburg, FRG, February 16-17, 1989. NH3Br (or C1) } (CH2)m, is H-['HN-CH-CO-]n -OH with m= 2,3,4 for poly(La, ?~diaminobutylic acid HBr), (DAB)n, poly(L-ornithine HCI), (Orn)~, and (Lys)n. Since a polypeptide has hydrocarbons in its side chains, various studies that determined changes in the secondary structure by the addition of salts [3][4][5] or an organic solvent [6][7][8][9], and the effect on the stability of the secondary structure by a surface-active agent [10][11][12] have been performed. Moreover, using (Lys)n the relationship between the number of hydrocarbons in a side chain and the secondary structure [13-161 has been investigated.…”

Peroxidase oxidations of hydroquinone and p-cresol in AOT reversed micelles

“…The change in the CD spectrum implies that the conformation of the enzyme changes largely as the water content in the reversed micelles decreases. As suggested in our previous papers, each amino acid residue of the polypeptide entrapped in the water pool interacts with the AOT molecule, and specifically takes part in governing the conformation of the polypeptide [25][26][27]. Therefore, the conformational change of the enzyme protein observed at each ZOo value seems to be attributable to the balance between the energy to maintain the native steric structure and the energy induced by the interaction of the amino acid residues of the enzyme with AOT molecules of the reversed micetles, and it is more remarkable as the Wo value becomes smaller, since the decrease of water content in the reversed micelle leads to the enhanced interactions with AOT molecules.…”

Conformational studies of the oligomers of L-lysine in reversed micelles

“…The reversed micellar solutions were prepared by the addition of the aqueous oligomers solution into an 0.05 M AOT/octane mixture as shown in previous articles [28,29], and the CD measurements were carried out on aJasco spectropolarimeter, model J-20. Figure 1 shows the CD spectra ofLys-15 inthe aqueous solutions containing various amounts of AOT.…”

“…This acceleration of enzymatic reaction is considered to be related to the conformational changes of proteins in the reversed micelles [20,23,25]. We have recently reported that the synthetic polypeptides such as poly(NS-dihydroxyethylaminopropyl-L-glutamine), poly(L-lysine), and poly(L-arginine) take an ordered structure in the reversed micelles, which depends upon the molar ratio of water to AOT, w0 [28,29].…”