Question

Pyruvate Dehydrogenase is a huge multi-enzyme complex in which substrates are channeled from one enzyme to the next. In fact, recent evidence suggests that many citric acid cycle enzymes may interact pass substrates along the pathway and that the components of the electron transport chain associate into an electron transfer super complex. What are the advantages of such an arrangement?

Answer 1

It is known as Multienzyme complexes-

The rate of an Biological reaction depends on the concentration of the enzyme and the concentration of its substrate in the Free Solution.
But What If Concentration Are Not Optimally Adequate.For Such an enzyme operating at suboptimal concentrations, the reaction is Known as diffusion-limited, because it depends on the random collision of the enzyme with it's substrate.
Let us take a metabolic pathway, in which the product of one reaction is going to be the substrate for the next reaction in the pathway. So Direct transfer will takes place if they are arranged in a chain fashion and this direct transfer of a metabolite from one reaction to another reaction will avoid dilution of the metabolite in the bulk aqueous medium and ultimately increase the rate of reaction.

In the cell, These kind of pathways are more common, enzymes of a particular pathway are frequently organised in Cell.
And This metabolic channelling can improve cell function.
Such enzymes association with one other involved in a particular pathway to form multienzyme complexes.
And such complexes, the diffusion of the substrate is not rate-limiting in the Cell.
Pyruvate dehydrogenase(PD) is a classical example if such complex . It is made up of three different enzymes that catalyse the oxidation of pyruvate sequentially.
It(PD) is comprising multiples of three different enzymes: eight of lipoamide reductase–transacetylase, six of dihydrolipoyl dehydrogenase and 12 of pyruvate decarboxylase, giving a total of 60 polypeptide chains per complex.

In eukaryotic cells, most of enzymes are effectively concentrated in particular parts of the cell in such a complexity. Major are proteins channel complex. So in this way concentration of enzymes can be achieved by specific protein–protein interactions.