ULTIMATE COMPUTING - Quantum Consciousness Studies

Protein Conformational Dynamics 131
necessary. A single coenzyme molecule can “turn on” the binding capabilities of
multiple subunits within an oligomeric enzyme (Roth and Pihlaja, 1977).
Examples of oligomeric enzymes include glutamate dehydrogenase,
composed of six 55 kilodalton subunits forming a complex with approximate
dimensions of 100 by 100 by 80 nanometers. An example of a more complex
oligomer is aspartate transcarbamylase. It contains six regulatory units of about
34 kilodaltons, each composed of 3 dimers. An additional six 100 kilodalton
catalytic subunits are each composed of two trimers. Six zinc atoms are necessary
in each of the regulatory subunits. Another cooperative oligomer is hemoglobin,
composed of two “alpha” and two “beta” subunits; many other oligomeric
enzyme patterns have also been observed. Oligomeric enzyme subunits have
cooperative interactions which means that the function of one subunit facilitates
the conformational actions of other subunits. In hemoglobin, conditions sufficient
for binding of one oxygen molecule to one subunit causes the remaining subunits
to bind oxygen more easily.
More complex protein assemblies include cytoskeletal polymers and virus
coats. The cooperative interactions of their subunits can lead to information
processing and thus to intelligent behavior.
6.2 Protein Conformation
At the tertiary structural level, most protein molecules are able to shift
reversibly between several different but related stable conformations and are
known as allosteric proteins. Such proteins may be able to form several
alternative sets of hydrogen bonds, disulfide bridges and Van der Waals forces of
about equal energy among their constituent amino acid side chains. Each
alternative set of intraprotein bonds and charge distribution requires a change in
the spatial relationships between components of the polypeptide chains and thus
motion occurs among the states. Only certain distinct conformations are
energetically favorable and any intermediate conformations are unstable and
unlikely. Charge redistribution (i.e. dipole oscillation) can also couple to
conformational switching. Thus step-like, nonlinear jumping occurs between
specific conformations so that only a discrete number of alternative
conformations exist for a given protein, and random switching from conformation
to conformation is limited.