Abstract
Calcium-dependent conformational changes of surfactant protein A (SP-A) and the collagenase resistant fragment (CRF) of SP-A were studied by measuring fluorescence spectra. The emission peaks of both SP-A and CRF in the absence of Ca 2+ appeared at 343 nm when they were excited at 280 nm. In the presence of Ca 2+, the peaks appeared at 340 nm and were accompanied by an increase in the fluorescence intensity. The magnitude of the fluorescence intensity change induced by Ca 2+ was amplified by the addition of dithiothreitol (DTT) in both SP-A and CRF. The Ca 2+ binding of CRF was measured by a flow dialysis method with 45CaCl 2 in the Ca 2+ concentration range where the Ca 2+-induced fluorescence changes occured. The maximum binding number of Ca 2+ to CRF was about 2 mol per mol of CRF, and the value was independent of the presence of DTT.
Published Version
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