Enzyme, design

Glycogen phosphorylase conforms to the Monod-Wyman-Changeux model of allosteric transitions, with the active form of the enzyme designated the R state and the inactive form denoted as the T state (Figure 15.17). Thus, AMP promotes the conversion to the active R state, whereas ATP, glucose-6-P, and caffeine favor conversion to the inactive T state. 

In the enzyme design approach, as discussed in the first part of this chapter, one attempts to utilize the mechanistic understanding of chemical reactions and enzyme structure to create a new catalyst. This approach represents a largely academic research field aiming at fundamental understanding of biocatalysis. Indeed, the invention of functional artificial enzymes can be considered to be the ultimate test for any theory on enzyme mechanisms. Most artificial enzymes, to date, do not fulfill the conditions of catalytic efficiency and price per unit necessary for industrial applications. 

One of the most direct questions to ask in the perspective of enzyme design is whether an already existing protein with a binding pocket might be turned into a new catalyst by introducing catalytic residues directly, rather than by the elaborated TSA mimicry approach used for catalytic antibodies, hoping to create a new biocatalyst that could harness both the activity and the selectivity, in particular stereoselectivity, that is possible with enzymes. 

Fig. 11.1. Somatic and secreted AChEs in N. brasiliensis. Extracts of parasites collected 4 days (track 1) and 8 days (track 3) post-infection of rats were resolved by non-denaturing PAGE alongside secreted products from parasites also collected 4 days (track 2) and 8 days (track 4) postinfection, and AChE activity visualized by cytochemical staining. Secretory enzymes designated as forms A, B and C are indicated, and the non-secreted isoform is arrowed. Reproduced from Hussein etal. (1999b), with permission.

This enzyme designation was formerly classified as EC 2.1.2.6. It is now classified under glutamate formimino-transferase [EC 2.1.2.5]. 

De novo design of proteins with pre-specified enzymatic activity is one of the most complex goals of protein engineering. So far only a few resnlts have been reported, but they are extremely interesting because they do prove that we are at the level where our insight into protein structure is sufficiently advanced to allow for de novo enzyme design. 

Fig. 20. Artificial enzyme design based on the concept of multiple recognition.

Perhaps only a few en2ymes (or none) exist in the body solely to take care of foreign chemicals. Many enzymes designed for normal-body substrates, however, apparently are capable of interacting with most mutagens and promutagens, the result is a complicated and delicate balance of detoxication and toxification, which may be highly dose-dependent (see for example, Dietz et oL, 1983). 

The pH optimum varies for different enzymes The pH at which maximal enzyme activity is achieved is different for different enzymes, and often reflects the [H+] at which the enzyme functions in the body. For example, pepsin, a digestive enzyme In the stomach, is maximally active at pH 2, whereas other enzymes, designed to work at neutral pH, are denatured by such an acidic environment (Figure 5.8). 

Lysosome. An organelle that contains hydrolytic enzymes designed to break down proteins that are targeted to that organelle. 

Durazym The First Enzyme Designed by Novo Nordisk," Soap, Cosmet. Chem. Spec., (Aug. 1991). 

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