Parkinson's disease and dopamines role

          Parkinson’s disease is a liberal neurological disorder which affects the motor system and thus individual’s ability to move. It is caused by the slow progressive degradation of neurons due to either genetic or environmental effects and the lack of dopamine in the substantia nigra of the brain. Dopamine is a neurotransmitter essential for the transfer of neuronal signals from the brain to the spinal cord and eventually to the appropriate muscles in the body. The shortage of dopamine in patients suffering Parkinson’s disease thus leads to the impairment of their muscular function. 

           Dopamine is produced from the conversion of L-tyrosine through the intermediate product dihydroxyphenylalanaine (L-DOPA) in step-wise process catalyzed by specific enzymes. This process occurs in the dopaminergic neurons of substantia nigra.

The following shows the complete 2-step reactions of dopamine production.

1)    Catalysed by tyrosine 3-monooxgenase

L-tyrosine + THFA  + O2 + Fe2+ → L-dopa + DHFA + H2O + Fe2+

2)    Catalysed by dopa decarboxylase

L-dopa + pyridoxal phosphate → dopamine + pyridoxal phosphate + CO2

           Any deficiencies of the substrates required for L-dopa formation such as L-tyrosine, iron and THFA (tetrahydrofolic acid) or for dopamine formation (from L-dopa) such as pyridoxal phosphate will lower the enzymes’ activity. This is evident in individuals with Parkinson’s disease in which the activity of either tyrosine 3-monooxgenase or dopa decarboxylase are as low as 20% (or less).The lack of one or more of the substrates also contributes to the damage of dopaminergic neurons by highly toxic superoxide anion produced by the resulting faulty reaction.