Cell Language Theory, The: Connecting Mind And Matter

80 The Cell Language Theory: Connecting Mind and Matter

b2861 The Cell Language Theory: Connecting Mind and Matter “6x9”

(see Figure 3.15). It is convenient to refer to the PSFP-based mechanism of

the substrate–enzyme interactions as the “pre-fit hypothesis” to contrast it

with the induced-fit hypothesis of Koshland [28] — “pre-fit” because

enzymes are postulated to have been selected by evolution (and hence carry

genetic information) on the basis of their ability to assume certain confor-

mational states capable of “capturing” or binding their elusive ligands as

they bump into their binding sites randomly through Brownian motions.

These two contrasting mechanisms of ligand binding processes are sche-

matically represented in Processes (3.10) and (3.11), where L stands for a

Figure 3.15 Induced-fit or pre-fit? “Enzyme changes shape by induced fit upon substrate

binding to form enzyme–substrate complex. Hexokinase has a large induced-fit motion

that closes over the substrates adenosine triphosphate and xylose. Binding sites in blue,

substrates in black and Mg^2 + cofactor in yellow. (PDB: 2E2N , 2E2Q )” Reproduced from

https://en.wikipedia.org/wiki/Enzyme. For the difference between the induced-fit and pre-

fit mechanisms, see text.

b2861_Ch-03.indd 80 17-10-2017 11:46:21 AM