The P34 protein is the main allergen for soybean sensitive humans. Soybean protein P34, a thiol protease belonging to the papain family, is a monomeric allergen having an N-terminal amino acid sequence and amino acid composition identical to that of the seed 34kDa protein. It is an insoluble glycoprotein having a pI of 4.5 and a calculated mass of 28.643 Dalton, representing 2–3% of total soybean protein. Upon glycosylation, the mass will be somewhat larger, resulting in a ~32kDa band in non-reduced SDS PAGE gels. It exhibits no enzymatic function due to an absence of the catalytic cysteine. P34 is stored in storage vacuoles of soybean cotyledons.