Amino Acid and Nitrogen Metabolism

What cofactor is required for transamination reactions?

Pyridoxal phosphate (PLP, from vitamin B6)

What is the role of glutamate in nitrogen metabolism?

Receives amino groups via transamination; can be deaminated to release NH₄⁺

What enzyme converts glutamate to glutamine?

Glutamine synthetase

Why is glutamine important in nitrogen transport?

Carries two nitrogen atoms safely in blood to liver/kidney

What cycle recycles alanine from muscle to liver for gluconeogenesis and nitrogen disposal?

Glucose-alanine (Cahill) cycle

What are glucogenic amino acids?

AAs that generate glucose precursors (e.g., pyruvate, oxaloacetate)

What are ketogenic amino acids?

Leucine AND Lysine(purely ketogenic) AAs that generate ketone precursors (e.g., acetyl-CoA, acetoacetate)

Which amino acids are purely ketogenic?

Leucine and lysine

What is Maple Syrup Urine Disease (MSUD)?

Deficiency of branched-chain α-ketoacid dehydrogenase,

Inc in Branched amino acids: Isoleucine, Leucine and Valine (I Love Vermont maple syrup from maple trees with branches)

Which amino acids accumulate in Maple Syrup Urine Disease?

Leucine, isoleucine, valine

Inc in Branched amino acids: Isoleucine, Leucine and Valine (I Love Vermont maple syrup from maple trees with branches)

What are symptoms of Maple Syrup Urine Disease?

Poor feeding, hypotonia, sweet-smelling urine, neurotoxicity

What is the purpose of the urea cycle?

Convert toxic NH₄⁺ to urea for excretion

Where does the urea cycle occur?

Liver (starts in mitochondria, ends in cytosol)

What activates carbamoyl phosphate synthetase I (CPS-I)?

N-acetylglutamate

What is the most common urea cycle disorder?

Ornithine transcarbamylase (OTC) deficiency

What lab finding distinguishes OTC from CPS-I deficiency?

Elevated urinary orotic acid in OTC deficiency

What are symptoms of urea cycle disorders?

Hyperammonemia, vomiting, lethargy, seizures, cerebral edema

CPS-1 Deficiency= no orotic acid

OTC Deficiency= orotic aciduria bc inc in carbamoyl phosphate

Which neurotransmitters are derived from tyrosine?

Dopamine, norepinephrine, epinephrine

Which neurotransmitters are derived from tryptophan?

Serotonin, melatonin

Which neurotransmitter is derived from histidine?

Histamine

Which neurotransmitters are derived from glutamate?

GABA (via decarboxylation) and glutathione

What causes phenylketonuria (PKU)?

Deficiency of phenylalanine hydroxylase or BH₄

What are symptoms of PKU?

Intellectual disability, hypopigmentation, musty odor

What causes homocystinuria?

Cystathionine β-synthase deficiency (most common)

What are symptoms of HOMOCYstinuria?

INC Homocysteine in urine, Osteoporosis, Marfanoid habitus, Ocular changes (downward Lens dislocation), Cardiovascular effects (thromboembolism), kYphosis(hunch)