Biosynthesis phosphorylase

The biosynthesis of purines and pyrimidines is stringently regulated and coordinated by feedback mechanisms that ensure their production in quantities and at times appropriate to varying physiologic demand. Genetic diseases of purine metabolism include gout, Lesch-Nyhan syndrome, adenosine deaminase deficiency, and purine nucleoside phosphorylase deficiency. By contrast, apart from the orotic acidurias, there are few clinically significant disorders of pyrimidine catabolism. 

Since D-fructose and D-glucose phosphates are amongst the first products of photosynthesis, and since starch (in plants) and glycogen (in animals) are converted by phosphorylase to D-glucosyl phosphate, biosynthesis of carbohydrates revolves around these ubiquitous compounds... 

Allosteric Enzymes Typically Exhibit a Sigmoidal Dependence on Substrate Concentration The Symmetry Model Provides a Useful Framework for Relating Conformational Transitions to Allosteric Activation or Inhibition Phosphofructokinase Allosteric Control of Glycolysis Is Consistent with the Symmetry Model Aspartate Carbamoyl Transferase Allosteric Control of Pyrimidine Biosynthesis Glycogen Phosphorylase Combined Control by Allosteric Effectors and Phosphorylation... 

Figure 18.14 Glycogen biosynthesis and degradation regulation. cAMP activates cAMP-dependent protein kinases. They cause the phosphorylation of glycogen synthase (inactivation), phosphorylase kinase (activation), and the inhibitory protein. The last inhibits phosphoprotein phosphatase. Activated phosphorylase kinase causes the phosphorylation of phosphorylase b, thus activating it to phosphorylase a. Phosphoprotein phosphatase is inhibited by the phosphorylated inhibitor protein. Such inhibition is released when the inhibitor protein is dephosphorylated. The phosphatase then reactivates glycogen synthase and inactivates phosphorylase kinase and phosphorylase a.

Other examples of PLP-requiring enzymes are the amino acid decarboxylases that lead to formation of amines, including several that are functional in nervous tissue (e.g., epinephrine, norepinephrine, serotonin, and y-aminobutyrate) cysteine desulfhydrase and serine hydroxymethyltransferase, which use PLP to effect the loss or transfer of amino acid side chains phosphorylase, which catalyzes phosphorolysis of the a-1,4-linkages of glycogen and cystathione beta-synthase in the transsulfiiration pathway of homocysteine. Additionally the biosynthesis of heme depends on the early... 

In nature a cascade of enzyme-catalyzed reactions is involved for the biosynthesis of starch. When selecting the appropriate enzymes and reaction circumstances reactions with multiple enzymes can be performed in vitro. Synthetic glycogen was first synthesized in vitro by Cori [146] in 1943 via the cooperative action of muscle phosphorylase and branching enzymes isolated from rat liver and rabbit heart. 

The exact way of amylopectin biosynthesis in plants is still not known today. In our current research we are using a tandem reaction of two enzymes to synthesize artificial amylopectin or rather (hyper)branched amylose in vitro. One enzyme is responsible for building the linear (amylose) part while the other enzyme introduces die branches, phosphorylase and glycogen branching enzyme respectively. 

---