Phosphoryl Transfer. In biological systems, the element phosphorous almost always exists as phosphate. Phosphorous is stable in several different oxidation states, but in phosphate, the oxidation state is +5. Therefore, the phosphorous atom in phosphate will always behave as an electrophile. - PowerPoint PPT Presentation
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In kinases, X is almost always ADP. However, GDP is known to substitute i some cases.
Sequential
1.ordered
2.random
Ping-pong
[B]
1/v
Vmax[A][B]
v =
Ka[B] + Kb[A] + [A][B]
1/[A]
[B]
Vmax[A][B]
1/v
v =
[A][B] + Ka[B] + Kb[A] + KaKb
1/[A]
Adenylate kinase displays a random ordered kinetic mechanism. In this case, the two substrates are bound randomly, and are in equilibrium with the “ternary complex” (E•MgATP•AMP). As in our derivation, this necessitates that the off rate for each of the substrates is less than the forward rate constant for the chemical step. This allows us to replace Km with Ks. However, it would not be incorrect to use Km values. Below is typical shorthand notation for kinetic schemes.
This is a special type of sequential mechanism in which MgUTP must bind firs, before glucose-1-phosphate. There is no degree of randomness. Ordered binding also implies ordered product release.