Lecture 6 Nitrogen digestion 2
Friday, 28 September 2012
Pyridoxal phosphate is a derivative of pyridoxine (B6)
Its major role is as a cofactor in transamination reactions
Present in meat, cereals, fruits and vegetables
Daily requirement 3 micrograms, dietary recommendation 100mg, toxic at levels of >100mg
Deficiencies rare, symptoms often neurological, mainly occurs in alcoholic and elderly people
Several forms of B6
Transported from muscles to liver combined with pyruvate to form alanine
Transported from brain to liver combined with glutamate to form glutamine
Ammonia reconverted in liver and detoxified to form urea.
CO2 + NH4+
Requires 2 ATP
Created by carbomyl phosphate synthase - biotin dependent as the cofactor
Used in the urea cycle with ornithine to produce citulline.
Refer to diagram
Comparative biochemistry of nitrogen excretion:
Humans are urotelic, we excrete most our nitrogen waste as urea. Urea is non toxic compared
to extremely toxic ammonia and it is water soluble.
Urea is fi