Indole-acetic acid binding proteins in soybean cotyledon.

Using the charcoal assay to separate free from bound hormone, the results showed that there is a high binding of IAA to cytosol proteins. Competition experiments were carried out using compounds with different auxin activity (indole-acetic acid, alphanaphtalene acetic acid, indole-butyric acid and phenyl-acetic acid), revealing that specificity of binding exists for those compounds with a molecular configuration appropiate for auxin activity. The protein nature of the indoleacetic acid-binding molecule was demonstrated by the use of enzymes and by its thermolability.