No abstract

By using synchrontron radiation small-angle X-ray scattering, we have studied the structure of biologial buffer/ sodium bis(2-ethylhexy1)sulfosuccinate (AOT)/2,2,4-trimethylpentane (isooctane) reversed micelles with varying water-surfactant molar ratio 00 (=[H20]/[AOT]), AOT concentration, and temperature. The scattering data were analyzed by several methods, including a shell modeling. Although in a high (00 range (16 < 00 -= 50) the obtained structural parameters of the AOT reversed micelle and the linear relation between the'water pool radius and the wo value are mostly in agreement with those determined by other authors, for 0 < wo < 12, however, discrepancies were found. These deviations can be understood by a transient oligomerization of reversed micelles, where with the increase of water content the micellar oligomerization proceeds successively from a metastable oligomeric phase to a stable monomeric phase through a transient phase. Increasing the AOT concentration and/or temperature reduced the reverse micellar dimension.

SynopsisFar-infrared spectra of poly-palanines having the a-helical conformation and the ,%form structure were measured. The spectra of glycine-L-alanine copolymer, silk fibroin, and copoly-D,calanines with different D : L compositions were also measured. In addition to the bands so far reported, four bands at 190, 167, 120, and 90 cm-1 were found for the a-helix conformation and the two bands at 442 and 247 cm-1 were found for the 6 form. The 442 cm-l band consists of the parallel 432 cm-l and perpendicular 445 cm-1 bands. The 247 cm-1 band is well defined and has strong dichroism parallel to the direction of stretching. These two bands appear also for silk fibroin and glycine-L-alanine copolymer. All the far-infrared bands of copoly-D,talanines can be interpreted as a-helix bands, the three peaks at 580, 478, and 420 cm-I being ascribed to the D-residue incorporated into the right-handed a-helix or to the tresidue in the left-handed a-helix.

The structure and reactivity of a-chymotrypsin solubilized in biological buffer-sodium bis(2-ethylhexyl)sulfosuccinate (AOT)-2,2,4-trimethylpentane (isooctane) reversed micelles, have been studied at various water/ surfactant molar ratios (coo) and protein concentrations using synchrotron radiation X-ray small-angle scattering and enzymatic activity measurements. Two types of a-chymotrypsins and two different substrates @-nitrophenyl acetate and p-nitrophenyl caprylate) were used. The scattering experiments show that a-chymotrypsins are entrapped in t h e water pools. In t h e low coo range (0 < coo < 12) oligomeric AOT reversed micellar formation occurs as a metastable state and simultaneously t h e enzymatic activity is enhanced significantly for both types of a-chymotrypsins, showing a maximum activity at coo = 12 for both substrates. The results from the scattering

A. FUJIE, T. K~MOTO, M. ~Y A , and T. KAWAI Es zeigte sich, daB die in Acetonitril wachsenden Ketten in Form der P-Modifikation auskristallisieren, sobald sie einen Polymerisationsgrad von 3 erreicht haben. Infolge der antiparallelen Anordnung der Ketten in der P-Modifikation scheint ein weiteres Wachstum der gebildeten Keime nicht moglich, so da13 auf der ,,Hauptkette" mit @-Modifikation die Ketten zunachst im amorphen Zustand weiterwachsen. Sobald die wachsenden Ketten jedoch einen Polymerisationsgrad von 10-13 erreicht haben, beginnen sie in Form der a-Helix zu kristallisieren. Infolge des topochemischen Charakters der Reaktion ist diese kritische Kettenlange, die zur Ausbildung der a-Helix notig ist, geringer als fur die entsprechenden bereits synthetisierten Oligomeren in Losung. Die im Anfangsstadium der Polymerisation gebildeten Keime mit P-Modifikation bleiben im weiteren Verlauf der Polymerisation erhalten.Der Polymerisationsverlauf in den Losungsmitteln Dioxan und Propionitril wurde ebenfalls untersucht. Ein Vergleich der Ergebnisse zeigt, daB der besonders giinstige Verlauf der Reaktion in Acetonitril durch eine Dipol-Dipol-Wechselwirkung zwischen Losungsmittel und Polypeptid bedingt sein konnte.