Kinase reactions

FIGURE 3.13 Phosphoenolpyruvate (PEP) is produced by the euolase reaction (hi glycolysis see Chapter 19) and hi turn drives the phosphorylation of ADP to form ATP in the pyruvate kinase reaction. 

ATP stores in muscle are augmented or supplemented by stores of phosphocreatine. During periods of contraction, phosphocre-atine is hydrolyzed to drive the synthesis of needed ATP in the creatine kinase reaction ... 

The problem can be solved using the equilibrium expression for the adenylate kinase reaction ... 

FIGURE 19.29 A mechanism for the pyruvate kinase reaction, based on NMR and EPR studies by Albert Mildvan and colleagues. Phosphoryl transfer from phosphoenolpyrnvate (PEP) to ADP occurs in four steps (a) a water on the Mg ion coordinated to ADP is replaced by the phosphoryl group of PEP (b) Mg dissociates from the -P of ADP (c) the phosphoryl group is transferred and (d) the enolate of pyruvate is protonated. (Adapted from Mildvan, A., 1979. Advances in Eiizymology 49 103-126.)... 

The middle panel shows the fall in PCr concentration in the muscle and the simultaneous increase in Pj released daring ATP degradation and resynthesis via the creatine kinase reaction ... 

The lower panel shows the decreasing concentration of ATP, to about 60% of resting levels, and the simultaneous equimolar increase in IMP. The fall in ATP started when most of the PCr store was utilized, resulting in a decreased rate of ADP phosphorylation via the creatine kinase reaction. The resultant accumulation of ADP stimulates adenylate kinase activity and subsequently IMP is formed via the AMP deaminase reaction ... 

Some Kinetic Parameters for Analogs of Creatine in the Creatine Kinase Reaction (71)... 

Kinases are enzymes that place a phosphate group on a serine/threonine or a tyrosine residue of a protein or peptide. All kinase reactions use ATP as the phosphate source. Therefore there have been assays developed that monitor the loss or gain of the peptide/protein substrate (LANCE, ULight) [23], the loss of ATP (easylite luminescence kinaseGlo, Perkin Elmer) [20], or the gain of ADP (Tran-screener TR-FRET) [24]. Many of these formats are applicable to cell based assays. 

Figure 3.6 Protein kinases. Selected amino acid residues within proteins are targets for kinases, (a) Tyrosine kinase reaction, (b) Serine/threonine kinase...

GNG exploits the fact that most of the reactions of glycolysis are reversible so the enzymes are shared between the two pathways. There are three kinase reactions (glucokinase/hexokinase, PFK and pyruvate kinase), which are not physiologically reversible are therefore the problem steps in the synthesis of glucose these three steps are overcome using alternative enzymes (Table 6.5, see also Section 1.7.1). 

Figure 6.47 Two phosphatase reactions to overcome kinase reactions...

The conversion of pyruvate into phosphoenolpyravate, which bypasses the pyruvate kinase reaction, requires two separate reactions carboxylation of pyruvate to... 

Synthesis and degradation of cychns Peptide and protein synthesis Protein kinase reactions Mitosis... 

In the last step, pyruvate kinase transfers this residue to ADP. The remaining enol pyruvate is immediately rearranged into pyruvate, which is much more stable. Along with step [7] and the thiokinase reaction in the tricarboxylic acid cycle (see p. 136), the pyruvate kinase reaction is one of the three reactions in animal metabolism that are able to produce ATP independently of the respiratory chain. 

The first steps of actual gluconeogenesis take place in the mitochondria. The reason for this detour is the equilibrium state of the pyruvate kinase reaction (see p. 150). Even coupling to ATP hydrolysis would not be sufficient to convert pyruvate directly into phos-phoenol pyruvate (PEP). Pyruvate derived... 

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