Question

4-Hydroxylation of spccific prolyl residues during collagen synthesis requires all of the following except A. \(\mathrm{Fe}^{2+}\). B. a specific amino acid sequence at the site of hydroxylation. C. ascorbic acid. D. co-hydroxylation of lysine. E. individual \(\alpha\) chains, not yet assembled into a triple helix.

Short answer

A. \(\mathrm{Fe}^{2+}\) B. Specific amino acid sequence at the site of hydroxylation C. Ascorbic acid D. Co-hydroxylation of lysine E. Individual \(\alpha\) chains, not yet assembled into a triple helix Answer: D. Co-hydroxylation of lysine

Step-by-step solution

Analyzing Option A - \(\mathrm{Fe}^{2+}\)

The 4-Hydroxylation of specific prolyl residues is catalyzed by prolyl 4-hydroxylase, an enzyme that depends on \(\mathrm{Fe}^{2+}\) as a cofactor to function correctly. Hence, \(\mathrm{Fe}^{2+}\) is required during this process.

Analyzing Option B - Specific amino acid sequence at the site of hydroxylation

Prolyl 4-hydroxylase carries out hydroxylation of specific prolyl residues only when they are present in a particular amino acid sequence. This is because the enzyme binds to its specific target sequences, thus making this option a requirement for the process.

Analyzing Option C - Ascorbic acid

Ascorbic acid (vitamin C) plays a crucial role in maintaining the stability of the \(\mathrm{Fe}^{2+}\)-containing enzyme, prolyl 4-hydroxylase. In the absence of ascorbic acid, the enzyme will lose its activity, and the hydroxylation process will not occur. Therefore, ascorbic acid is also a requirement for this process.

Analyzing Option D - Co-hydroxylation of lysine

The hydroxylation of lysine residues occurs in collagen synthesis as a separate process catalyzed by the enzyme lysyl hydroxylase. This process is not directly related to the 4-Hydroxylation of specific prolyl residues and is not a requirement for the prolyl hydroxylation process.

Analyzing Option E - Individual \(\alpha\) chains, not yet assembled into a triple helix

During collagen synthesis, individual \(\alpha\) chains undergo hydroxylation before they assemble into a triple-helix structure. Thus, hydroxylation of proline and lysine residues occurs on individual \(\alpha\) chains before the formation of the complex collagen structure. This makes option E a requirement for the process.

Conclusion

Based on the analysis of each option, the only option that is not a requirement for the 4-Hydroxylation of specific prolyl residues during collagen synthesis is Option D - co-hydroxylation of lysine.