Tryptophan synthetase of E.coli, a typical bifunctional oligomeric enzyme consists of

The correct option is two proteins designated A and B.

Tryptophan synthetase (or tryptophan synthase) in Escherichia coli is a classic example of a bifunctional oligomeric enzyme system. It is a multi-subunit complex that catalyzes the final two steps in the biosynthesis of the amino acid L-tryptophan from chorismate.

Structurally and functionally, the enzyme is organized as follows:

1. Subunit Composition: The active tryptophan synthase complex is a heterotetramer with an ${\alpha }_2{\beta }_2$ subunit structure. This complex is composed of two distinct proteins (polypeptide chains):
- The alpha (α) subunit (often historically referred to as protein A).
- The beta (β) subunit (often historically referred to as protein B).

2. Functional Cooperation: The α protein (subunit A) catalyzes the cleavage of indole-3-glycerol phosphate to indole and glyceraldehyde-3-phosphate. The β protein (subunit B) catalyzes the subsequent condensation of indole with L-serine to produce L-tryptophan. Indole is channeled directly from the α-active site to the β-active site through an internal molecular tunnel.

Thus, the complete, typical bifunctional oligomeric enzyme of E. coli consists of two distinct proteins designated as A (or α) and B (or β) working in concert.