Studies on the thermal dissociation of glycerol dehydrase

Abstract

It has previously been shown that the interaction of the apoenzyme of glycerol dehydrase with Li or Na ions produced a reversible dissociation into two different, separately inactive protein subunits, A and B. On the other hand the formation of the complex AB · B 12OH between hydroxocobalamin and the associated apoenzyme AB, strengthens the binding of A to B so that effective dissociating agents for the apoenzyme, such as Li, Na, or EDTA, do not cause dissociation. Dissociation of AB · B 12OH can be achieved, however, if the complex is heated to over 60 °. Heating produces an active subunit B, an inactivated subunit A, and a B 12 derivative. Li and Na ions promote this thermal dissociation while K, Rb, Cs, and NH 4 ions inhibit it, in descending order. When the separated subunits are heated individually; subunit A is very heat labile and is somewhat stabilized against heating by high concentrations (of the order of 2 m) of Na +, Rb +, K +, and Cs +, but not by Li + at any concentration tried; while subunit B is stabilized against heat by K + and is made more labile to heat by Na + or Li +. Potassium ions inhibit heat-mediated dissociation of AB · B 12OH complex. Potassium ions may thus aid the association, while sodium or lithium ions may promote dissociation, by virtue of their effects on the conformation of subunit B in the AB · B 12OH complex.