passages.id: split_5_test_375_passage
passages.type: progene_text
passages.text: When mixed together , peptides N1 + C1 form a thermostable ( Tm > 90 degrees C ) , 82 % alpha-helical , discrete trimer of heterodimers ( mass 31 , 300 M(r) ) that is resistant to denaturation by 2 % SDS at 40 degrees C .