偶然路过，顺便为我的G宝盘作宣传，但是我的资料从不收钱，有网管又不高兴就删了这贴吧。+ K& ~/ x+ B! N! a: l
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下面回答别构酶定义：
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" y: A$ T5 P. ?5 Y! L“Allostery, or a “different shape,” is the coupling ofconformational changes between two widely separated
/ C1 C: R+ X# j4 X4 xsites. Allosteric proteins have two identical (homotropic) or1 f% A' K5 L$ K( `3 l) t
different (heterotropic) ligands. The binding of one ligand
' H, C. V% F) C0 aincreases (or decreases) the affinity of the protein toward
4 h# D; K: T7 o1 a7 C) fthe second . The two binding sites may be on the( k& q! J( z; \
same polypeptide chain though in different domains, or in& E0 c" M7 o. n; |6 v8 K5 A
different subunits. Allostery is crucial to living cells. It has) ~3 \2 @. ~7 i! a) U
long been shown to control metabolism either throughpositive feedback regulation or negative inhibition. In 1965, Monod et al. analyzed 24 allosteric enzyme systems
8 [- o& o2 u) r2 w5 W8 H F# Kand proposed a “plausible model on the nature of allosteric
& ?6 g2 v3 N+ c0 m" L. Ptransition” (the “concerted” or “MWC” model).5 The proposition
/ I* m& x' p9 f1 X3 ^8 Ywas inspired by the observation of two conformational- B+ ?3 i0 M% |4 q# A& \; ]2 B
states of deoxy- and oxyhemoglobin. The MWC: \ K. H6 B) Z; ^6 S2 v
model suggested that allosteric proteins are symmetric
8 g2 s' t! S: s+ z, a- b: B" A7 moligomers with identical protomers. Each protomer exists
! L5 J5 U2 v: U7 P; Gin “at least” two conformational states (tense, T; relaxed, @* d; C, {5 u/ V+ p# S# j, x
R) with different affinities for ligands.5 The basic assumption " A9 t) j# M# ]: T0 \2 O
of the model is that the protein interconverts between5 k; I) Z. s) y) q& S& W
two conformations, R and T, in a concerted manner.
8 J- J9 S) X& X& M0 C; r0 vSubunits in the oligomers cannot exist in a hybrid form6 o& K9 O$ \( P. ~' g; K4 J
such as TR. Koshland et al. challenged the MWC model2 {' ]$ {+ n7 b7 s4 N5 M0 L
and proposed their sequential hypothesis (the “KNF” or “sequential” model).6 In the sequential model, subunits
( V0 _- m1 t/ `) schange conformation, one at a time. Thus, a hybrid form) }/ _5 a4 O0 o: q
such as TR can exist in the sequential model. Here, the
; I8 f9 z; ~, [: Zbinding of a ligand will change the conformation of a
. F' A5 G3 k. D$ z5 vprotomer without affecting the neighboring subunits. Eigen
. d+ Q3 D; S4 P& \, C Xcombined the MWC and KNF extreme models leading to a general model.7 However, decades of research have! K+ Q7 R8 g2 f, b% o7 B2 u
lead to the conclusion that the exact mechanisms by which
+ [! o9 c6 ~& y% P1 R! Callostery is achieved may span a broad range, and can be
1 l& }) A3 O: h! A3 kextremely different from each other, although a few prototypes do exists.”
/ g9 j6 K7 x- W From:K. Gunasekaran, Buyong Ma,1and Ruth Nussinov,Is Allostery an Intrinsic Property of All Dynamic Proteins?PROTEINS: Structure, Function, and Bioinformatics 57:433–443 (2004). $ m- I8 T" C3 K) c& r: Y4 n1 F% K
( w7 x* F u' ]* f[ 本帖最后由 班昭 于 2007-5-29 08:55 编辑 ]
