Phosphoryl transfer creatine kinase

A good example of an affinity label for creatine kinase has been presented (35). This enzyme catalyzes the reversible transfer of a phosphoryl group from adenosine triphosphate [56-65-5] (17) to creatine [57-00-1] (18), leading to adenosine diphosphate [7584-99-8] (19) and phosphocreatine [67-07-2]... 

An example of a random, single-displacement mechanism is seen in the enzyme creatine kinase, a phosphoryl-transfer enzyme that uses ATP as a phosphoryl... 

Creatine (N-methylguanidoacetic acid) and its phosphorylated form creatine phosphate (a guanidophosphate) serve as an ATP buffer in muscle metabolism. In creatine phosphate, the phosphate residue is at a similarly high chemical potential as in ATP and is therefore easily transferred to ADP. Conversely, when there is an excess of ATP, creatine phosphate can arise from ATP and creatine. Both processes are catalyzed by creatine kinase [5]. 

In the course of studying the mechanism of action of creatine kinase from rabbit skeletal muscle (M.M isoenzyme), Kenyon and coworkers (4,90) have been involved in the design of specific irreversible inhibitors that are active-site-directed (affinity labels). Creatine kinase catalyzes the reversible transfer of a phosphoryl group ( the elements of "POi") from ATP to creatine, as shown in the following reaction ... 

Kinases Direct transfer of terminal phosphoryl group of ATP to substrate Creatine kinase Adenylate kinase Hexokinasc Phosphoglycerate kinase Pyruvate kinase Protein kinase Myokinase Phosphofructokinase Type 1 (M-S-E) Type 1 Type 1 Type 1 Type 2 (S-M-E)... 

The amount of ATP in muscle suffices to sustain contractile activity for less than a second. Creatine phosphate in vertebrate muscle serves as a reservoir of high-potential phosphoryl groups that can be readily transferred to ATP. Indeed, we use creatine phosphate to regenerate ATP from ADP every time that we exercise strenuously. This reaction is catalyzed by creatine kinase. 

As implied above, a dissociative or Sul mechanism for phosphoryl transfer is more difficult to establish than an Su2 mechanism. An SnI mechanism may be operative in the reaction catalyzed by creatine kinase as suggested by the observation that planar trigonal monoanions such as nitrate and formate (54) which are analogs of metaphosphate, (Fig. 5)... 

Since metal coordination or immobilization of the transferred phosphoryl group by multiple hydrogen bonds would inhibit the formation of a metaphosphate intermediate in an S l mechanism and would facilitate nucleophilic attack in an Sy2 mechanism, the latter process seems likely for the reactions catalyzed by staphylococcal nuclease, DNA polymerase, pyruvate kinase, fructose diphosphatase, phosphoglucomutase, (Na + K) ATPase and possibly PEP carboxylase. In creatine kinase where an S l mechanism is possible, the enzyme would have to prevent access of nucleophiles other than ADP and creatine to the reactive metaphosphate intermediate. 

Phosphoryl group transfer from creatine phosphate to ADP is catalyzed by the enzyme creatine kinase. 

As its high phosphate transfer potential suggests (see Figure 3.7), this compound is capable of phosphorylating ADP very efficiently. The reaction is catalyzed by the enzyme creatine kinase as follows ... 

The use of paramagnetic probes in magnetic resonance studies on phosphoryl transfer enzymes, e.g. creatine kinase, has been reviewed, and model reactions with phosphoroguanidates have led to new ideas on the mechanism of action of this enzyme. The pH-rate profile for the... 

Metal cofactors do not always bind to the enzyme but rather bind to the primary substrate. The resulting substrate-metal complex binds to the enzyme and facilitates its activity. Creatine kinase catalyses the transfer of phosphoryl groups from adenosine triphosphate (ATP), which is broken down to adenosine diphosphate (ADP). The reaction requires the presence of magnesium ions. These, however, do not bind to the enzyme but bind to ATP, forming an ATP Mg complex. It is this complex that binds to the enzyme and allows transfer of the phosphoryl group ... 

Biosynthesis of ATP. ATP is the irrunediate product of all cellular processes leading to the chemical storage of energy. It is biosynthesized by phosphorylation of ADP in the course of Substrate phosphorylation (see). Oxidative phosphorylation (see) and non-cyclic Photophosphorylation (see) in plants. Energy in the form of a third phosphate may also be transferred to ADP from other high-energy phosphates, such as creatine phosphate (see Creatine) or other nucleoside triphosphates, or in the adenylate kinase reaction. 

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