ANALYSIS OF QUATERNARY PROTEIN ENSEMBLES BY MATRIX-ASSISTED LASER DESORPTION IONIZATION MASS-SPECTROMETRY/

The intact noncovalent structure of the homo-oligomeric complexes of s treptavidin (52 kDa), alcohol dehydrogenase (150 kDa), and beef Liver catalase (240 kDa) have been observed using the matrix 2,6-dihydroxyac etophenone in an organic solvent. Intact streptavidin tetramers could also be observed with ferulic acid and other hydroxyacetophenone deriv atives. Intact complexes are observed only for the first shot al a giv en position, which may be due to physical segregation or precipitation of the noncovalent complexes at the crystal surface. This effect is i ndependent of the macroscopic crystal structure or the type of substra te (hydrophobic versus hydrophilic). Observation of intact complexes i s not affected by addition of less than 10 mM salts or buffers, and ap pears to be independent of the pH stability-range of the protein sampl es investigated. (C) 1997 American Society for Mass Spectrometry.