What enzyme's function is decreased due to vitamin C deficiency in a patient whose diet consists only of crackers?

Vitamin C, also known as ascorbic acid, plays a crucial role as a cofactor in the post-translational modification of collagen, which is essential for its stability and functionality. One of the key enzymes that require vitamin C for its activity is prolyl 4-hydroxylase. This enzyme is responsible for the hydroxylation of proline residues in collagen, a process that is critical for the formation of stable collagen fibers.

In the case of vitamin C deficiency, the function of prolyl 4-hydroxylase is significantly impaired, leading to defective collagen synthesis. This results in weakened connective tissue and contributes to symptoms such as easy bruising, poor wound healing, and other manifestations related to scurvy.

While other enzymes listed may have significant functions in their respective metabolic pathways, they do not directly relate to the consequences of vitamin C deficiency in the same way that prolyl 4-hydroxylase does. Therefore, the decreased function of prolyl 4-hydroxylase due to a lack of vitamin C is the most pertinent answer in this context.