title: Preliminary structural comparison of the proteinase isoinhibitors IIA and IIB from bull seminal plasma based on individual assignments of the 1H nuclear magnetic resonance spectra by two-dimensional nuclear magnetic resonance at 500 MHz.
abstract: By combined use of amino acid analysis, chemical sequence determination for the N-terminal decapeptide and two-dimensional 1H nuclear magnetic resonance at 500 MHz the amino acid sequence of bull seminal inhibitor IIB was found to coincide with that of the isoinhibitor IIA, except that the N-terminal tripeptide Pyrl-Gly2-Ala3- in HA is replaced by the dipeptide H-Leu2-Phe3- in IIB. Nearly complete, individual proton assignments were obtained for the isoinhibitor IIB, and comparison with the previously obtained corresponding nuclear magnetic resonance data for the isoinhibitor IIA showed that the two proteins must adopt closely similar secondary and tertiary structures in aqueous solution. The individual resonance assignments provide a basis for future, more detailed investigations of the influence of the local primary structure differences on the protein conformation.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D006023:Glycoproteins; D009682:Magnetic Resonance Spectroscopy; D011480:Protease Inhibitors; D011487:Protein Conformation; D012661:Semen
chemical_list: C027399:BUSI II protein, Bos taurus; D006023:Glycoproteins; D011480:Protease Inhibitors