L-Dopa converts to dopamine by a decarboxylase enzyme. B6 is necessary for this enzyme to work. B6 will bind to the enzyme to make it active to convert L-Dopa to dopamine. When B6 gets depleted it becomes more and more difficult to get adequate amounts of dopamine.
B6 is also needed 5HTP to covert to serotonin. So when B6 is depleted, many people experience symptoms like depression. B6 is required for over 300 other enzymatic reactions in the body. So B6 is essential for dopamine, serotonin and other needed chemical production.