Sip1 Protein (IMAGE) Technical University of Munich (TUM) Caption The small heatshock protein Spi1 exists in three forms comprising 24, 28 and 32 identical subunits. Acidic conditions shift the equilibrium towards the active forms with 24 and 28 subunits. Credit Image: Tilly Fleckenstein / Sevil Weinkauf / TUM Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.