Download Transamination, Deamination,urea cycle

Transamination,
Deamination,urea cycle
24-5-13
• Transamination & deamination reactions
Transamination
• α- ketoglutrate plays vital role in amino acid
metabolism by accepting amino groups from
most amino acids becoming glutamate
• Glutamate become deaminated or used in the
formation of non essential amino acids
• location
• exception of lysine & threonine
Most important Amino Transferases
• ALT: transfers amino group of alanine to
alpha-ketoglutrate hence forming pyruvate &
glutamate
• AST: transfers amino groups from glutamate
to oxaloacetate forming aspartate ( N source
in urea cycle)
• Plasma ALT, AST can be elevated in hepatic
and non hepatic diseases i.e. Myocardial and
muscle disorders
• Deaminations
Glutamate dehydrogenase causes the
oxidative deamination of amino acids
liberation free ammonia (NH3)
• Glutamate ---the only amino acid that
undergoes rapid oxidative deamination
• NAD+ or NADP+ as a coenzyme
• (GTP) is an allosteric inhibitor of glutamate
dehydrogenase, whereas (ADP) is an activator
• When energy levels are low in the cell, amino
acid degradation by glutamate dehydrogen
ase is high, facilitating energy production
Urea cycle
• first two reactions leading to the synthesis of
urea occur in the mitochondria, whereas the
remaining cycle enzymes are located in the
cytosol
• One nitrogen of the urea molecule is supplied
by free ammonia, and the other nitrogen by
aspartate
Ammonia disorders
• The two major causes of hyperammonemia
(with its CNS effects) are liver disease and
inherited deficiencies of enzymes (such as
ornithine transcarbamolyase) in the urea
cycle
Overall stoichiometry of the urea cycle
• Aspartate + NH3+ CO2+ 3 ATP + H2O → urea +
fumarate + 2 ADP + AMP + 2 Pi + PP