BIOC L7- nitrogen metabolism II

When does amino acid catabolism occur?

high protein diet, insufficient protein diet (kwashiorkor), insufficient energy diet

What is kwashiorkor?

when energy intake is sufficient but protein intake is insufficient, causes swelling of facial tissues and stomach as albumin protein in blood usually holds water but if deficient water not held in blood and spreads to tissues

What are aminotransferases?

enzymes which move amino groups from an AA to its corresponding ketoacid to form a new AA, requires pyrodixal phosphate which is derived from B6

What are transaminases?

a type of aminotransferase which cannot perform the reverse reactions

What are the important amino acid-keto acid pairs to remember?

a-ketoglutarate and glutamate, oxaloacetate and asparatate, pyruvate and alanine

What is the role of aspartate transferase?

catalyse reaction transferring amino group from aspartate to a-ketoglutarate to form glutamate and oxaloacetate

What is the role of alanine transferase?

catalyse reaction tranferring amino group from alanine to a-ketoglutarate to fomr glutamate and pyruvate

What are AST and ALT markers of?

liver damage such as cirrhosis (scarring), fatty liver disease

Why are aminotransferase enzymes important?

when amino acids are in short supply can be made or safe removal of excess amino groups

What is the reaction between glutamate to glutamine?

adds NH4+ and involves glutamine synthetase, requires ATP

Where is the NH4+ for the reaction from glutamate to glutamine sourced from?

deamination of glutamate in most tissues, GABA (brain), or AMP (muscle)

What is the reaction from glutamine to glutamate?

removal of 1 of the 2 N groups glutamine carries, involves glutaminase

What is the reaction from glutamate to a-ketoglutarate?

2nd step of glutamine deamination, involves glutamate dehydrogenase

What are the 3 ways amino groups can be deaminated?

transaminations: shuttling amino groups from AAs to ketoacids, oxidative deamination: glutamate dehydrogenase, hydrolysis: glutaminase

How is N transported in most tissues?

amino acids trnafer their N group to glutamate, this has a NH4+ group added involving glutamine synthetase to form glutamine which goes to the liver

How is N transported in the liver?

glutamine enters and is deaminated to glutamate by glutaminase, NH4+ group whch is removed goes into urea

How is N transported in muscle?

amino acids transfer their N group to glutamate which gives it to pyruvate forming a-ketoglutarate and alanine which moves to the liver

What happens with the glucose-alanine cycle starting in the liver?

alanine donates amino group to a-ketoglutarate forming glutamate which is deaminated and NH4+ is excreted in urea resulting in a-ketoglutarate again, alanine has become pyruvate which enters glucoeneogenesis to form new glucose which goes back to muscle where it is broken down into pyruvate and the cycle begins again