โ Scribed by Jeffrey L. Browning; Robert J. Mattaliano; E.Pingchang Chow; Shu-Mei Liang; Bernard Allet; Joseph Rosa; John E. Smart
No coin nor oath required. For personal study only.
Native interleukin-2 (IL-2) contains three cysteines; two exist in a disullide bridge (Cys-58 and Cys-105) and the third Cys-125 is a free sullhydryl. In the presence of 6 M guanidine hydrochloride at alkaline pH, IL-2 is converted into three isomers. Each isomer represents one of the three possible disulfide-linked forms that can be generated from three cysteines. These three isomers were resolved on a C4 reverse-phase HPLC system. The identity of each of the three forms was determined by carboxymethylation of the free cysteines in each isomer with [3H]iodoacetic acid followed by determination of the labelled cysteines by tryptic peptide mapping. Tryptic peptide mapping of the more predominant of the two scrambled peaks showed it to be the Cys-105-S S-Cys-125 linked form of IL-2. A Ser-125 construction of IL-2, which lacks a free cysteine, did not scramble under these conditions. These experiments demonstrate the utility of reverse-phase HPLC in studies of protein folding and disulfide bond structure. o 1986 Academic PFZSS, hc.
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## Abstract From the crude mixtures of isomeric 4โnitrophenylthieno[2,3โ__b__]pyridines (**3**) previously reported [1] were isolated three analytically pure samples, __viz.__ the 2โisomer (yellow needles, mp 258ยฐ, **3a**), the 6โisomer (red prisms, mp 182ยฐ, **3e**), and a ternary mixture of the 2โ