Identify the First Step in the Mechanism for the Vitamin

Multiple Choice

Identify the first step in the mechanism for the vitamin KH₂-dependent carboxylation of glutamate.

A) The vitamin K base removes a proton from the gamma-carbon of the gluatamate.
B) The vitamin loses a proton from a phenolic OH group.
C) The dioxetane collapses to form a vitamin K base.
D) The base attacks molecular oxygen.
E) The glutamate carbanion attacks carbon dioxide.