Effects of pH, temperature and Ca2+ content on the conformation of alpha-lactalbumin in a medium modelling physiological conditions.

Data obtained by the intrinsic protein fluorescence technique showed that, in addition to Ca2+ and Mg2+ ions, bovine alpha-lactalbumin also binds physiologically significant Na+ and K+ ions, the nucleotides ATP, ADP, UTP, UDP and UDP-galactose. The release of the bound Ca2+ ions from the protein in a medium modelling physiological conditions (containing Mg2+, Na+, K+, ATP and ADP in physiological concentrations) induced a transition of the protein from the native state of the Ca2+-loaded form to a state which is a mixture of native and and thermally changed states of the apo- and metal bound forms. Any variations in temperature result in changes in the populations of these states. This may be associated with some Ca2+ and temperature dependent regulation of the protein function. Variations of pH within the physiological limits had little influence on the conformation of both Ca2+-loaded and Ca2+-free alpha-lactalbumin.