Protein Metabolism III: Sulfer and Aromatic Amino Acid

Question 1

sulful containing AA

Answer 1

cysteine (unessential)

methionine (essential

Question 2

cysteine function

Answer 2

structural integrity of proteins (esp extracellular)

important role in redox potential
glutathione: tripeptide that controls redox potential via reversible reaction
Gsh–> Gssg

Question 3

Methionine

Answer 3

produces intermediate in cysteine production: SAM

Question 4

SAM

Answer 4

major carbon donor & high energy storage unit like ATP

Question 5

Recycling MET rxn

Answer 5

MET>SAM>SAH>Homocysteine>Met
MET>SAM>SAH>Homocysteine>Crystathione>Cysteine

• Homocystein>Met requires THF and Vitamin B12 to transfer back CH3 group
• Homocysteine>Crystathione enzyme defective in homocystinuria, enzyme also requires B6

Question 6

hyperhomocystemia

Answer 6

cause: low folate, B6, B12, vascular disease

Description: CV disease

AA: Cysteine becomes essential

Treat: Folate, B6, B12

Question 7

homocystinuria

Answer 7

cause: defective CBS: can’t convert homocysteine>cysteine
description: mental retardation, osteoporosis, lens subluxation, tall with kyphosis, vascular disease, thrombosis, atherosclerosis (MI & Stroke)

AA: cysteine becomes essential

Treat: supplement B6 to force CBS activity

Question 8

cysteinuria

Answer 8

cause: hereditary deficit of renal PCT and intestinal AA transporters for COLA (cysteine, ornithine, lysine, arginine)

Description: kidney stones/ failure

Diagnose: urinary cyanide nitroprusside test

Treat: Urinary alkinization (potassium citrate, acetazolamide); chelating agents

Question 9

CBS enzyme

Answer 9

requires B6

Question 10

reaction homocysteine> met

Answer 10

requires THF, vitamin B12

Question 11

THF overview

Answer 11

¬ Synthesized in bacteria
¬ Precursor to folate
¬ One carbon group in any oxidative state is bonded to N-5 or N-10

Question 12

THF Forms

Answer 12

Most reduced Form: methyl group
Oxidized Form: methylene group
Most Oxidized Form: methenyl, formyl, formin, or no group

Inter-convertable forms used to donate carbon in many reactions

Question 13

GSH overview

Answer 13

¬ Redox Buffer
¬ Highly soluble tripeptide as opposed to Cys
¬ Milimolar in some tissues

Question 14

GSH Functions

Answer 14

Thiol redox buffer = SH buffer; proteins in reduced form/ regulate activity

Enzyme cofactor for Gst (glutathione transferase)

Reduce Hydrogen peroxide to water; H202 H20; protects against ROS

Question 15

Metabolism Products of tryptophan, phenylalanine, tyrosine

Answer 15

tryptophan: pyruvate or acetoacetate

Phenylalanine & tyrosine: fumerate or acetoacetate

Question 16

Tryptophan Rxn

Answer 16

Tryptophan Hydroxylase: cofactor BH4

Trp»» serotonin (NT); melatonin (hormone); niacin (energy)

Question 17

Phenylalanine Rxn

Answer 17

Phenylalanine hydroxylase: Cofactor BH4, deficient in PKU

Phe > Tyr

Question 18

Tyrosine Rxn

Answer 18

Tyrosine hydroxylase: cofactor BH4

Tyr>Dopa»> Catecholamines (dopamine, NE, epinephrine)

Question 19

PKU

Answer 19

Cause: deficient Phe hydroxylase or BH4 cofactor (malignant)

Description: excessive Phe leads to excess phenylketones in urine; Intellectual disability, growth retardation, fair skin, eczema, musty body odor

AA: tyrosine becomes essential

Screen: 2-3 days after birth/ after mom’s enzyme gone

Treat: decrease dietary Phe and increase tyrosine; avoid aspartame which contains Phe

Question 20

maternal PKU

Answer 20

lack of proper therapy during pregnancy

Infant: microcephaly, intellectual disability, growth retardation, congenital heart defects

Question 21

Akaptonuria

Answer 21

cause: deficient homogentisate oxidase in tyrosine degradation pathway to fumate

Description: dark connective tissue, brown pigmented scalar, urine black with exposure to air; debilitating arthralgia because homogentisic acid is toxic to cartilage

Treatment: low Phe diet with tyrosine

Question 22

Albinism

Answer 22

cause: defect in Tyrosine metabolism and therefore deficiency in melanin production

Complete albinism: deficit tyrosinase

description: decreased pigmentation of eyes, hair, skin

Question 23

Parkinson’s

Answer 23

dopamine is reduced in parkinson’s

one treatment is l-dopa which is dopamine precursor

Question 24

MAOIs

Answer 24

MAO breaks down products of dopamine, NE, epinephrine, serotonin

hypertensive crisis with tyramine rich foods like cheese