Phosphotransferases covalent intermediates

The Permease Systems of Bacteria. The best defined of these is the galactoside permease of E. coli. This transport system mediates the active accumulation of galactosides in the presence of metabolic energy and the facilitated diffusion of these compounds when the energy system is blocked (8). A specific galactoside-binding protein has been implicated, but it seems clear that the system is different from the phosphotransferase system described above since no covalent intermediates of... 

Frey PA (1992) Nucleotidyltransferases and phosphotransferases stereochemistry and covalent intermediates. In Sigman DS (ed) The enzymes, vol 20, Mechanisms of catalysis. Academic Press, San Diego, p 141... 

The rationale for the different mechanisms of the other paired reactions [(36a) and (36b) and (37a) and (37b)] is exactly the same. This pattern is followed by all enzymes of this class. That is, nucleophilic catalysis and covalent intermediates, which are necessary and required for the Ping-Pong kinetic pathway to operate, are found only in those cases involving Ping-Pong kinetics. No phosphotransferase or nucleotidyltransferase is known to catalyze phosphoryl or nucleotidyl group transfer by a sequential kinetic pathway via a doubledisplacement mechanism. However, it is not certain that in all cases of double... 

A few nucleotidyltransferases and phosphotransferases act by mechanisms that include a covalent nucleotidyl-enzyme or phosphoenzyme as a compulsory intermediate. A few more ATP-dependent synthetases act by such mechanisms. However, the overwhelming majority of these enzymes catalyze phosphoryl or nucleotidyl group transfer by mechanisms that entail the direct, one-step transfer of the nucleotidyl group or phosphoryl group between two substrates bound in adjacent subsites at the active site. 

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