Phosphorylase structure

FIGURE 15.15 (a) The structure of a glycogen phosphorylase monomer, showing the locations of the catalytic site, the PLP cofactor site, the allosteric effector site, the glycogen storage site, the tower helix (residnes 262 throngh 278), and the snbnnit interface. 

After more than 20 years, Walde et al. (1994) returned in a way to coacervate experiments, although using other methods. Walde (from the Luisi group) repeated nucleotide polymerisation of ADP to give polyadenylic acid, catalysed by polynucleotide phosphorylase (PNPase). But instead of Oparin s coacervates, the Zurich group used micelles and self-forming vesicles. They were able to demonstrate that enzyme-catalysed reactions can take place in these molecular structures, which can thus serve as protocell models. Two different supramolecular systems were used ... 

Hajdu, J., Pombradi, V., Bot, C., and Friedrich, P. (1979) Structural changes in glycogen phosphorylase as revealed by cross-linking with bifunctional diimidates Phosphorylase b. Biochemistry 18, 4037-4041. 

Habash, J. R. Helliwell, J. D. Stoeckler, R. E. Parks, Jr., S. F. Chen, and C. E. Bugg, Three-dimensional structure of human erythrocytic purine nucleoside phosphorylase at 3.2 A resolution, J. Biol. Chem. 265 1812 (1990). 

Secrist, S. Y. Babu, C. E. Bugg, W. C. Guida, and S. E. Ealick, Structure-based design of inhibitors of purine nucleoside phosphorylase, 3,9-arylmethyl derivatives of a 9-deazaguanine substituted on the methylene group, J. Med. Chem. 36 3771 (1993). 

Muscle glycogen phosphorylase is one of the most well studied enzymes and was also one of the first enzymes discovered to be controlled by reversible phosphorylation (by E.G. Krebs and E. Fischer in 1956). Phosphorylase is also controlled allosterically by ATP, AMP, glucose and glucose-6-phosphate. Structurally, muscle glycogen phosphorylase is similar to its hepatic isoenzyme counterpart composed of identical subunits each with a molecular mass of approximately 110 kDa. To achieve full activity, the enzyme requires the binding of one molecule of pyridoxal phosphate, the active form of vitamin B6, to each subunit. 

In the majority of cases, fluorescent labels and probes, when studied in different liquid solvents, display single-exponential fluorescence decay kinetics. However, when they are bound to proteins, their emission exhibits more complicated, nonexponential character. Thus, two decay components were observed for the complex of 8-anilinonaphthalene-l-sulfonate (1,8-ANS) with phosphorylase(49) as well as for 5-diethylamino-l-naphthalenesulfonic acid (DNS)-labeled dehydrogenases.(50) Three decay components were determined for complexes of 1,8-ANS with low-density lipoproteins.1 51 1 On the basis of only the data on the kinetics of the fluorescence decay, the origin of these multiple decay components (whether they are associated with structural heterogeneity in the ground state or arise due to dynamic processes in the excited state) is difficult to ascertain. 

The darkest inner box in Fig. 93 includes those classic doubly wound parallel sheets that exactly match the topology of lactate dehydrogenase dl. Phosphorylase domain 2 is a five-layer structure in... 

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