[Stabilizing effect of oligomerization on aldolase protomers in rabbit muscles]

It is shown by the fluorimetric analysis that with the 1,2 M MgCl2-induced dissociation of rabbit muscle aldolase the tertiary structure of the resulted protomers (subunits) remains practically unchanged. Significant changes in the protomeric enzyme are provoked by subsequent addition of urea up to the concentration of 2,3 M, and are, evidently, manifested in a significant decrease in regularity of the hydrophobic part of aldolase and in possible transition of its Trp-147 into more polar environment. This transition is reflected in the longwave shift of the protein fluorescence maximum (lambda max) by 13 nm (from 320 to 333 nm). But the joint action of MgCl2 and urea does not lead to complete unfolding of the resulted protomeric enzyme. More deep structural alterations in the subunits occur on acidic dissociation, and lambda max shift in this case reaches 342 nm. Structural changes caused by MgCl2 and urea are concomitant with the increase of fluorescence quenchibility with NADH. Here a short-wave lambda max shift, being usually observed in native aldolase fluorescence quenching, is not registered. This mean that the photoselection of protein fluorophores does not occur. The results thus obtained produce an evidence that oligomerization endows aldolase protomers with enhanced stability.