Cell Language Theory, The: Connecting Mind And Matter

The Bhopalator 93

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

Gould [180, p. 319] describes PMR in another way:

... if a given sequence of steps constitutes the favored mechanism for

the forward reaction, the reverse sequence of these steps constitutes the

favored mechanism for the reverse reaction.... (3.19)

Enzymologists often write a generalized enzyme reaction thus:

S + E ↔ S•E ↔ P + E, (3.20)

a b c

where E is the enzyme, S the substrate, and P the product. Clearly Scheme

(3.20) is not microscopically reversible, since the sequence of events fol-

lowed in the direction from left to right is not the same as that from right

to left. There is no P∙E in the scheme. In order to modify Scheme (3.20)

so as to make it microscopically reversible, it is necessary to use GFCP

(Section 2.7) as shown in Scheme (3.21):

S + E ↔ S + E* ↔ S•E* ↔ [S•E‡ ⇔ P•E‡] ↔ P•E* ↔ P + E* ↔ P + E, (3.21)

a b c d e f g h

where E* and E‡ represent the so-called Franck–Condon states of the

enzyme which are conformationally strained high-energy states in thermal

equilibrium with their associated ground states [70]. Of the two Franck–

Condon states, E* is long-lived (with lifetimes thought to be much longer

than ~ 10 -^12 s, the typical time required for electronic transitions) and E‡ is

short-lived lasting long enough for electronic transitions to take place as a

part of a chemical reaction, i.e., covalent rearrangements. Hence we may

refer to E* and E‡ as “stable” and “unstable” Franck–Condon states, the

latter often symbolized by square brackets, [...] [6, 12, 14]. Evidently,

Scheme (3.21) is microscopically reversible, i.e., the scheme is mechanis-

tically symmetric with respect to the inversion around the symbol ⇔.

There are several unusual features about Scheme (3.21) that require a

special attention:

(1) Enzymes are postulated to undergo thermal fluctuations between

their ground state, E, and energized states, E* (called “stable Franck–

Condon states”) in the absence of its substrate.

b2861_Ch-03.indd 93 17-10-2017 11:46:25 AM