HYDROGEN-EXCHANGE KINETICS OF REDUCED ALPHA-LACTALBUMIN BOUND TO THE CHAPERONIN GROEL

alpha-Lactalbumin in which all the disulfide bonds are fully reduced ( RLA) is known to bind strongly to the chaperonin GroEL, Although RLA i s more unfolded than the native state and the molten globule state of alpha-lactalbumin, the CD spectrum of RLA in the far-UV region shows t hat RLA is not fully unfolded but has an appreciable amount of seconda ry structure, To investigate whether the secondary structure elements present in RLA are responsible for the recognition of RLA by GroEL or not, we have examined the hydrogen-exchange kinetics of RLA in the pre sence and absence of GroEL, Our results show that the hydrogen-exchang e kinetics of RLA bound to GroEL is identical to that of free RLA, Thi s implies that the secondary structure elements in RLA are not importa nt for the recognition by GroEL, but the unstructured parts of RLA tha t are not relevant to the stability of the secondary structure provide strong recognition sites of RLA.