1. role in storage high energy phosphate in muscle ... crp

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5 Creatine Creatinine

• 1. Outline biosynthesis of creatine creatinine
• 2. Role of phosphocreatine in ATP homeostasis
• 3. Creatinine excretion in urine

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Phosphagens

• 1. Role in storage high energy phosphate in
  MUSCLE
• 2. ATP ADP small reserve (not stored as
  fuels)
• 3. Most cells ATPuse ? ATPsyn
• Muscle ATPuse gtgt ATPsyn
• 4. Phosphagens also provide directionality
  (control), increase in ATP would affect all cell
  processes
• 5. Vertebrates Phosphocreatine
• Some invertebrates phospho Arg

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Synthesis of Creatine
(i) 3 AA are involved in syn GLY, ARG, MET (as
SAM) (ii) First RXN Transamidinase transfers
amidine (H2N-CNH2) group from ARG to GLY ?
guanidinoacetate ornithine. (ii) Second RXN
guanidinoacetate undergoes methylation (CH3) via
SAM ? creatine This RXN represents the major use
of SAM in the body (quantitatively). More SAM is
used than in all other methyl rxns (gt 50)
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Synthesis of Phosphocreatine

• Creatine ATP ADP creatine-P (phosphagen)
  enzymecreatine kinase
• (i) At rest RXN? (ATP demand low)
• At work ? RXN (ATP demand increases)
• (ii) Creatine kinase ? functional availability
  of ATP and directionality (only phosphorylates
  ADP)
• (iii) ATP is immediate donor free energy, rapid
  turnover must be rapidly generated

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ATP / Phosphocreatine Energetics

• (i) ATP is a high energy compound ?G -7.3
  kcal/mol
• (ii) Phosphocreatine also high energy ?G -10.3
  kcal/mol
• (iii)Phosphocreatine is a compound designed to
  keep ATP constant
• Where creatine-P ADP ? Creatine ATP
• Keq products / substrates 54 where ?G
  -3
• CrP ? Cr ATP? ADP
• Resting muscle 20 10 5.94 0.055 mM
• Working muscle 2 28 4.52 1.17 mM
• 54 Keq resting 10 5.94 working 28
  4.52
• 20 .055 ?2 1.17?
• Stable Thus ATP remains at 76 original
  although
• Variable creatine - P decreased 10x (10)

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ENERGY USAGE
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Formation of Creatinine

• (i) Spontaneous cyclization occurs ? creatinine
• Occurs at a relatively constant rate
• Creatinine excreted in urine ? constant and ?
  muscle mass
• (ii) Amount creatinine excreted urine ? time over
  which sample is taken measurement of total
  creatinine in 24 h urine collection indicates
  accuracy of collection
• (iii) Creatinine increases with
• elevated catabolism in muscle
• increase in muscular dystrophy

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Creatine Kinase
Creatine Kinase (muscle enzyme) increase with
muscle damage. CK exists as isozymes (MM, MB,
BB) Only MB is found in the heart (15 of total
CK) Measured in blood (after trauma) Index of
myocardial infarction muscle trauma
muscular dystrophy severe muscular exertion
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5. Creatine  Creatine Kinase and Myocardial
Infarction Case Discussion
An obese, middle-aged man was brought to the
emergency room following an automobile accident.
The patient stated that he had been short of
breath and very dizzy just before the crash.
Examination suggested either a cerebrovascular
accident or a myocardial infarction. The patient
was admitted for observation, and blood samples
for creatine kinase (CK) and other enzyme assays
were periodically collected.
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Discussion
1. Using a reaction described in this chapter,
how might CK be assayed? 2. What is the relation
of CK activity in the blood to tissue damage?

• 1. Assay creatine kinase using artificial
  substrate (instead of creatine)
• creatinine ATP ? H which can be measured
  through changes in pH

2. Diagnostic Value CK is present in all tissues
but only SELECTIVE RELEASE (brain, muscle but not
liver) therefore different from liver
damage Caused byMI, muscle trauma, muscle
dystrophy, severe exertion, IM injections,
hypothyroidism, chronic alcoholism (with myopathy)
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Discussion
3. What would be the advantage of measuring
heart-specific isozyme and how could the isozymes
of CK be differentiated? 4. What is the purpose
of assaying for CK over a period of time?

• 3. Isozymes creatine kinase are tissue specific
• CK is a dimer of MM, MB, BB isozymes, and only
  MB is present in the myocardium (15 TOTAL CK)
• Analysis by antibody assay specific for isozymes
  (which can differentiate between proteins)

4. MB-CK myocardial specific injury - 100
increase in MB-CK within 4 hr although total
blood CK may be N (Why?) - Peaks at 8-24 hr then
decreases, with aminotranserase change much
slower ? peak 60hrs (To maximize treatment,
prompt recognition essential) - Usually CK
cardium MB/total CK are constant, MB-CK?
is proportional to degree injury to myo cardium