鸭肝脂肪酸合成酶的胍变性与失活

报道了鸭肝脂肪酸俣成酶在胍变性过程中构变性过程中构象变化和活性变化的关系，首次验证了邹承鲁提出的酶活性部位构象的理论适用于多功能复合酶，同时该酶变性及复性均可测定出多个阶段，且证明有无活性稳态酶存在，在低浓度盐酸胍溶液中该酶的全反应活性和其中两个还原部位单独活性被同步可逆抑制，随着胍浓度增高，出现不可逆失活且程度和速度均迅速提高，在０．５４ｍｏｌ／Ｌ胍中该酶全反应活性在１．５分种内已有一半不可逆失

THE DENATURATION AND INACTIVATION OF FATTY ACID SYNTHASE FROM DUCK LIVER IN GUANIDINE HYDROCHLORIDE

The denaturation and inactiVation of fatty acid synthase (FAS) fiom duck liver bygUaindine hydrochioride (GndHCl) solution of different concentlation was studied. The overall activity and two nduction activities of FAS were reversibly inhibital by low conCentlationof GndHCl (below 0.45mol/L). Inactivation of the enzyme folioed an elhance of GndHClconcentlation. Half of the ovelall reaction activity was lost within l.5 Ininuthe in 0.54Inol/LGndHO, and 5% achvity remained at the end of inachvation. The inactivation involved twopad. The inactiVation of overan reaction activity was much mere breater and fastef than theinactiVation of reductions in the same condition and GndHCI conCentration. The overed reaction activity could be recovered by dilution ac fast pad inactiVatal by GndllCI, but not after second phase inactiVation in that phase the nductions were also inactivatal. The adults suggest that there are some stable unactive confonnations in the enzyme.The incease of UV absorbance of FAS, decrease in intheity and red shift of its intrinicfluorescence in GndHCl occur in two stages from 0.72 to 1.08mol/L and 2.16to 2.88mol/LGndHCl aspectively. A similarity was shown for its CD change. About 20% of the totalthiols of intaCt FAS natal rapidly with 5,5' -dithiobis (2-nitrobenzoic acid), and are believed to be suiface thiols . The total SH reacted rapidly with DTNB for the 2.88mol/LGndHCl treated FAS. Ihactivatoin occuring at a lower GndHCl concentration than that required for notiasble conformation changes suggests that the achve site of FAS is located in alimited region more fragile than the molecule as a whole.