The present invention relates to thermostable proteases having an amino acid sequence which homologous to the amino acid sequence of proteases derived from Nocardiopsis, and the production thereof by wild-type and recombinant host cells including transgenic plants and non-human transgenic animals. The proteases are effective in animal feed, in particular fish feed, and detergents. The proteases are capable of degrading the soybean Bowman-Birk inhibitor, and other antinutritional factors such as soybean agglutinin and the Kunitz trypsin inhibitor, as well as the isolated soy storage proteins glycinin and beta-conglycinin. Characteristic structural features of relevance for the thermostability of these proteases of peptidase family S2A or S1E are disclosed.