Which of the following enzymes is believed to be deficient in Parkinsonism?

Answer is B (Tyrosine Hydroxylase): Tyrosine Hydroxylase is the most impoant (critical) enzyme, deficiency which leads to Parkinson's disease The main biochemical charachteristic of Parkinson's Disease is the reduction of neurotransmitter and the dopamine synthesizing enzyme system including Tyrosine Hydroxylase (7'H) and Tetrahydrobiopterin (BH4) Cofactor in nigrostriatal neurons. `The loss of Tyrosine Hydroxylase represents the critical failure in Parkinson's Disease because this enzyme is the rate limiting enzyme dopamine synthesis. With a deficiency of tyrosine hydroxylase the ever-shrinking pool of nigrostriatal tract neurons cannot sustain the essential synthetic pathway. Once approximately 80% of these neurons degenerate, the nigrostriatal tract cannot synthesize adequate dopamine and Parkinson's disease symptoms appear' - 'Clinical Neurology for Psychiatrits'.