Studies on cell-clearing activity in alpha-lactalbumin. Effects of calcium removal on activity and conformation.
Effects of calcium removal on the cell-clearing activity of alpha-lactalbumin (alpha-LA) and concomitant changes in conformational structure have been investigated as part of a continuing study of the activity found earlier [McKenzie, H.A. & White, F.H., Jr. (1987) Biochem. Int. 14, 347]. This activity is similar to that of lysozyme, whereby lysis of the bacterial cell wall is catalyzed. However, the specific activity of alpha-LA is on the order of 10(-6) that of lysozyme. Under conditions where activities of apo and native alpha-LA were approximately linear functions of the protein concentration, the maximal ratio of apo to native activity was 5.7:1, determined by comparison of second order velocity constants. The CD spectrum of apo alpha-LA is intermediate between that of the A state and the native protein. By NMR, the conformation of apo alpha-LA is similar to, but distinctly different from, that of the native protein. The apo form did not revert completely to the native state when Ca(II) was resupplied, consistent with a role for this cation in folding. It is suggested that the activity increase may result from a diminished constriction of the "cleft" region in alpha-LA.
White
F H
FH
Chemistry Department, Florida State University, Tallahassee.
D002118:Calcium / Q000494:pharmacology*; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D009113:Muramidase / Q000378:metabolism; D011487:Protein Conformation / Q000187:drug effects
D007768:Lactalbumin; D009113:Muramidase; D002118:Calcium