Chemical structure GSAO and GSCA and Dose-dependent increase of PWBC protein tyrosine phosphorylation induced by GSAO. A and B. The boxes indicate the region of the molecule thought to be primarily responsible for the biological activity of GSAO and the corresponding region in the control GSCA. Oxidation of GSAO is possible. The resulting molecule (GSAA) is thought to be inactive, but may become active again, if reduced in vivo. To avoid oxidation, GSAO solutions are prepared freshly, or stored after snap-freezing at -80°C. No significant activity loss of deep-frozen GSAO was observed for up to 6 months. PWBC were treated with GSAO or GSCA where indicated for 24 h and tyrosine phosphorylation detected by western blot. C 50 μM GSCA does not alter the protein pTyr levels of PBWC detectably. D Changes in protein pTyr patterns are apparent with as little as 1.5 μM GSAO. GSAO-affected proteins are indicated with arrows.