Inhibitor of Rac family GTPases. Blocks activation by direct binding to Rac1, Rac1b, Rac2 and Rac3 (KD values are 40, 50, 60 and 250 nM respectively). Inhibits Rac, Ras and Tiam-induced growth transformation of NIH-3T3 fibroblasts. Reduces β-amyloid peptide production in vivo.