The major enzyme that catalyzes the reduction of carbon dioxide in photosynthesis is called ribulose-1,5-bisphosphate carboxylase/oxygenase (commonly known as Rubisco).

Here's why:

* Carbon dioxide fixation: Rubisco is the key enzyme in the Calvin cycle, which is the process by which plants convert carbon dioxide into sugars.

* Carbon dioxide as a substrate: Rubisco binds to carbon dioxide and catalyzes its incorporation into a molecule called ribulose-1,5-bisphosphate (RuBP).

* Reduction: The resulting molecule is then reduced and eventually converted into glucose.

While other enzymes are involved in the process of carbon dioxide reduction, Rubisco is the primary and most important one.