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Sulphur Containing Amino Acids
E T B O L Sulphur Containing Amino Acids They are methionine,cyseine,cystine. Methioinine is essential. It serves as precursors for the synthesis of cysteine and cystine. Both are non essential. Cysteine and cystine are interconvertable. The sulphur-containing AA are an exclusive dietary source of sulphur in the body
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Sulphur containing Amino Acids
E T B O L Sulphur containing Amino Acids Cystine Cysteine Methionine CH3 S (CH2)3 Methionine CHNH2 COOH
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Methionine and cysteine present in proteins.
B O L Methionine is essential ,it serves as precursor for the synthesis of cysteine and cystine. Methionine and cysteine present in proteins. The sulfur containing amino acids are almost an exclusive dietary source of sulfur to the body.
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Methionine (Amino Acid that form Succinyl CoA)
B O L Methionine (Amino Acid that form Succinyl CoA) It is one of four amino acids that form succinyl CoA. It is converted to s-adenosylmethionine(SAM),the major methyl- group donor in one carbon metabolism. . It is also a source of homocysteine – a metabolite associated with atherosclerosis and vascular disease.
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Metabolism of Methionine
c d S M E T B O L Metabolism of Methionine 3 parts Utilization of methionine for transmethylation reactions. Conversion of methionine to cysteine and cystine. Degradation of cysteine and its conversion to specialized products
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Cysteine Biosynthesis Cysteine is synthesized from essential A.A.
Metabolism of Sulphur containing Amino Acids(Cystein, cystine Methionine: Cysteine Biosynthesis Cysteine is synthesized from essential A.A. methionine Ist Step: ATP+Methionine S-Adenosyl methionine SAM serve as precursor for methyl group ex. Nor epinephrine Epinephrine Methionine adenosyl transferease
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A m I n o c d S M E T B O L
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A m I n o c d S M E T B O L S-Adenosylmethionine is highly reactive due to the presence of a positive charge. The enzyme involved in the transfer of methyl group are called methyltransferase. S-AM transfer the methyl group to an acceptor and gets itself converted to S- adenosylhomocysteine. The loss of free energy in this reaction makes the methyl transfer irreversable.
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m I n o c d S M E T B O L A 2nd step:
S-Adenosylmethionine S-Adenosyl homocysteine SAM release its methyl group to a methyl acceptor forming S- Adenosyl homocysteine
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A m I n o c d S M E T B O L
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m I n o c d S M E T B O L A 3rd Step: S-Adenosyl homocystinase
S-Adenosyl homocysteine Homocysteine+ Adenosine S-Adenosyl homocysteine is cleaved by the homocysteinase enzyme to give homocysteine and adenosine need H2O and doesn't need any catalytic action. S-Adenosyl homocystinase
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S-Adenosylhomocysteine is hydrolysed to homocysteine and adenosin
B O L S-Adenosylhomocysteine is hydrolysed to homocysteine and adenosin
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m I n o c d S M E T B O L A 4th Step:
Homocysteine + Serine Cystathionine This step is a condensation of homocystine with AA serine to form cystathionine need catalytic enzyme synthetase Cystathionine synthetase
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Fate: Cysteine is needed for protein synthesis and other body need.
m I n o c d S M E T B O L Cystasthionine lyase 5th step: Cystathionine Cysteine+ α ketobutyrate Lyses of cysthionine to form cysteine and αketobutyrate by the enzyme cystathionine lyase. Fate: Cysteine is needed for protein synthesis and other body need. αketobutyrate is decarboxylated to propionyl CoA.
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Degradation &resynthesis of methionine
c d S M E T B O L Degradation &resynthesis of methionine
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Homocysteine has 2 fate: Fate of homocysteine
d S M E T B O L After donation of the methyl group ,S- Adenososylhomocysteine is hydrolysed to homocystein and Adenosine. Homocysteine has 2 fate: Fate of homocysteine If there is a deficiency of methionine ,homocysteine may be remethylated to methionine. Or if there is adequate amount of methionine ie stores are adequate homocysteine may enter the transsulfuration pathway ,where it is converted to cysteine
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Fate1: if inadequate stores of methionine
c d S M E T B O L Fate1: if inadequate stores of methionine Homocysteine accept a methyl group from N –methyl THF in a reaction requiring methylcobolamine (co B12) . The methyl group is transferred from B12 derivative to homocysteine
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Degradation &resynthesis of methionine
c d S M E T B O L Degradation &resynthesis of methionine
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A m I n o c d S M E T B O L
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Metabolic Diseases Related to Sulphur Amino Acids
Homocysteinuria: # It is related to methionine metabolism. # It is autosomal recessive disease. #It is inborn error of metabolism due to deficiency of Cystathionine synthetase. .(step 4). #Accumulation of homocystine and Its appearance in the urine. # Cataract, Mental retardation, Taller than other group.
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#Harmful treatable disease if diagnosed early.
c d S M E T B O L #Harmful treatable disease if diagnosed early. #Diagnosis by amino acids analysis in the urine. #Increase homocystine in the urine. #Treatment is supply of milk with no methionine and added cystein.
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Relationship of homocysteine to vascular disease
B O L Relationship of homocysteine to vascular disease Elevation of homocysteine accelerate oxidative damage inflammation and endothelial dysfunction ,and independent risk factor for occulsive vascular disease. Epidemiological studies have shown that that plasma homocysteine is inversly related to the plasma levels of folate, B12 and B6 ,the three vitamine that involved in the conversion of homocysteine to methionine and cysteine Supplementation of these vitamines has been shown to reduce circulating levels of homocysteine .
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Relationship of homocysteine to vascular disease
B O L Relationship of homocysteine to vascular disease In addition large elevation of homocysteine in blood as a result of rare deficiency in cystathionine synthetase are seen in patients with classic homocysteinuria . These individuals experience premature vascular disease with about 25% dying from thrombotic complications before 30 years of age.
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#Autosomal recessive inherited abnormality of tubular reabsorption.
Cystinuria #Autosomal recessive inherited abnormality of tubular reabsorption. #Excessive excretion of dibasic amino acids cystine, ornithine,arginine &lysine (25-40)times normal. #The defect is in the renal reabsorption mechanism
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#precipitate to form renal calculi. (cystine calculi).
d S M E T B O L Cystinuria #Cystine is relatively insoluble and become of a high concentration in the urine. #precipitate to form renal calculi. (cystine calculi). #Diagnosis by demonstrating excessive excretion of cystine in the urine. #Management is to prevent calculi formation by reducing urine concentration. High fluid intake, urinary alkalinizer , penicillamine.
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Cystinosis #Rare but serious disorders of cystine metabolism.
#Excessive deposition of cystine in different organ, kidney, bone marrow, cornea, conjunctiva. #Generalized aminoaciduria with glucosuria. #Harmful untreatable disease end with early death. #Defect is unknown, may be due to impaired in the transport of cystine from the affected cells.
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A m I n o c d S M E T B O L Creatinine # It is one of the final product of Arginine, Glycine & Methionine. #Creatine present in muscles, brain& blood. #Creatinine is the anhydride of creatine formed by irreversible non enzymatic dehydration of muscle creatine.
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m I n o c d S M E T Arginine Glycocyamine B O L A
Schematic presentation of creatinine biosynthesis NH2 C NH4 Arginine-glycine transamidination Arginine Glycocyamine Kidney ATP 5-Adenosylmethionine ADP 5-Adenosylhomocystine Muscle- non enzymatic dehaydration Creatine phosphate Creatinine H2O+pi
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A m I n o c d S M E T B O L Creatinine is normally released from skeletal muscles to the circulation in a constant manner and excreted through complete filtration without reabsorption.
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Interpretation of serum creatinine should consider certain factors:
B O L Interpretation of serum creatinine should consider certain factors: 1. Lower in children than adult, lower in female than male & lower during pregnancy . 2.Certain drugs(salicylate&cimitidine) increase creatinine by inhibiting tubular secretion of creatinine. 3.Some endogenous substances (acetoacetate) may affect the analytical method of measurement of creatinine
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Increase in serum creatinine is likely due to a fall in GFR.
B O L Serum Creatinine is indirect measurement of Glomerular Filtration Rate (GFR) Increase in serum creatinine is likely due to a fall in GFR.
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Increase serum Creatinine( Decrease GFR) could be due to:
1.Any diseases lead to impairment of renal perfusion. 2.Diseases lead to loss of the functioning nephrons (Acute&chronic glomerulonephritis). 3.Diseases whose pressure is increased on tubular side of the nephrons.
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Increase in serum creatinine is likely due to a fall in GFR.
B O L Serum Creatinine is indirect measurement of Glomerular Filtration Rate (GFR) Increase in serum creatinine is likely due to a fall in GFR.
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A m I n o c d S M E T B O L Creatinine can be used for in the measurement of creatinine clearance (index of GFR) UV PX1440 U: Urine Creatinine. V: 24 hours urine volume. P: Plasma creatinine. I440: 24X60
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Normal Range: Serum Creatinine(0.6-1.4)mg/dl.
B O L Normal Range: Serum Creatinine( )mg/dl. Creatinine Clearance:(80-120)ml/min. .
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