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Aam 7 metabolism of sulphur containing a.a's
1. Metabolism Of Sulphur Containing
Amino Acids
By
N. Santhosh Kumar
Asst. Professor
Department of Biochemistry
Shridevi Institute of Medical Sciences & Research
Hospital
2. Thiol (-SH )
group
Disulfide (-S-S- ) group
Sulfur (-CH3-S- ) group sulfur-containing, essential,
glucogenic amino acid.
Non essential, glucogenic
amino acid.
7. Re-methylation
methyl transferase
N5N10 Methylene
FH4
N5N10 Methylene
reductase
One
carbon pool
In vitamin B12 deficiency the defect
in the conversion of methyl THF results
in trapping of THF as methyl-THF, this
is called as folate trap
N5
9. Trans Methylation Reaction
SAM acts as donor of methyl group
Methionine active form is S-adenosyl methionine
(SAM)
Transfer of methyl group from SAM to acceptor
molecules
16. Imp of Cysteine
Component of proteins & essential for disulfide bonds,
which stabilize protein structure
Imp dietary source of sulfur: involved in the syn
Sulfolipids, Glycosaminglycans, sulfated steroids
Conversion of Cysteine to pyruvate –involved in the
formation of glucose
Involved in Bile acids synthesis (taurocholate)
17. Imp of Cysteine
Synthesis of Coenzymes-A
(Acetyl CoA, Succinyl CoA, HMG-CoA, Fatty acyl CoA)
Involved in the formation Glutathione
(Glutamate+Cysteine+Glycine = G-SH)
Involved in detoxification mechanisms
(Chlorobenzene, Iodobenzene, Naphthalene are
detoxified to mercapturic acids & excreted in urine)
Taurine acts as inhibitory neurotransmitter in CNS
19. CYSTINURIA (Cystin-lysinuria)
• Common inborn error of amino acid transport
• Defect in impaired reabsorption of dibasic amino
acids(Cystine, ornithine, Arginine &lysine (COAL)
Clinical feature :
• Abnormal excretion of COAL
• formation of Cystine Calculi in renal tubules
• Leads to obstruction, infection & renal
insufficiency
20. Treatment
Injection of large amount of water,
Increased cystine solubility through maintenance of
alkaline urine
21. Diagnosis
Cyanide- Sodium Nitroprusside Test
• It is a screening test.
• Urine is made alkaline with ammonium hydroxide and add sodium
cyanide.
• If Cystine present, is reduced to cysteine.
• Then add sodium nitroprusside to get a magenta-red color complex.
• Specific aminoaciduria may be confirmed by chromatography.
22. • Rare but serious lysosomal Storage
disorder
• Caused by defect in transport of Cystine
across the lysosomal membrane from
lysosomal vesicles to cytosol
• leading to Cystine accumulates in the
lysosomes in many tissues and forms
crystals impairing their functions.
CYSTINOSIS
(cystine storage disease)
24. Identified by Nitroprusside test & microscopy of blood
shows Cystine crystals in WBC, Flat crystals in urine
Adequate fluids for increased urine out put
Diagnosis
Treatment
Alkalization of urine by sodium benzoate & administration of
antibiotic D-penicillamine
25. Homocystinuria
A group of methionine metabolic disorders
High blood and urinary levels of homocysteine &
methionine
27. Homo
cystinuria
Defect of the enzyme Symptoms
Type- I Cystathionine
Synthase
Ectopia lentis (dislocation of the lenses in
the eyes), skeletal abnormalities,
osteoporosis, thinning & lengthening of the
long bones & thrombosis
Diagnosis :
Cyanide sodium nitroprusside test
Treatment :
Therapy with Pyridoxine (to activate
cystathionine β- synthase)
low methionine & supplemented with
cystine diet
Type -II Methylene-THFA
reductase
Type -III deficiency of methyl
Vit B12
Type- IV malabsorption of Vit
B12
28. Case Based Question-1
A 20year old man came to the emergency room with severe pain in his
right side and back. Subsequent examination and evaluation indicated a
kidney stone and increased excretion of cystine, arginine and lysine in
the urine
Questions:
a. What is the probable diagnosis?
b. What is the biochemical defect?
c. What are the complications of this disorder?
d. How is the condition to be treated?
Pankaja Naik. Protein Metabolism. Textbook of biochemistry.4th Ed. Case History-04: p-299
29. Case Based Question-2
A 12year old girl presented to paediatric OPD with mental
retardation, difficulty in walking because of Charlie Chaplin’s gait.
On fundoscopic examination lens was dislocated. Cyanide sodium
nitroprusside test on urine sample was positive.
a: What is probable diagnosis?
b:What is the enzyme defect in above condition?
c: Which vitamin coenzymes are involved in this condition?
d: Which amino acid is not synthesized in this condition ?
30
Wilma Delphine silvia et al. OSPE& CBL .Competency Based Practical Biochemistry Text book, 2nd ed.; case-8: p146
30. Case Based Question-3
A 22year old male is brought to the hospital with a complaint of
hematuria and severe pain in his lower right flank. Urine
examination revealed elevated levels of cystine, ornithine, Arginine
& lysine. Microscopic examination showed hexagonal crystal
deposit. Urine exam was positive for the cyanide nitroprusside test.
Further X-rays showed the presence of stones in kidney.
a: What is probable diagnosis?
b:What is the enzyme defect in above condition?
c: What is the causes for this disorder?
d: Which amino acid is not synthesized in this condition ?
31
Rafi et al. Text book of Biochemistry, 4th ed: case- study - 6: p296
