Number of isoenzymes in LDH enzyme -
(D) (5) (65 Harper 29th) * LDH has 5 isoenzymes while CPK has three. * LDH is an oligomeric (tetrameric) enzyme made up of four polypeptide. * Two types of subunits namely M (for muscle) is basic and H (for heart) is acidic. * LDHi has more positive charge and fastest in electrophoretic mobility while LDHS is slowest. * LDH5 has low Km (high affinity) while LDH1 has high Km (low affinity) for pyruvate. * Normal CSF LDH is 5 to 40 U/L. Similar to AST (Aspartate transaminase). Increase of CSF LDH observed in abscess, cerebral haemorrhage / infarction and metastatic carcinoma. * Increase of LDH4 isoenzyme of CSF has been reported in tubercular meningitis. * Normal serum LDH activity ranges from 60 to 250 IU/L (120 - 500 units / mL) Behavior in Acute MI In acute MI, serum activity rises within 12 to 24 hours attains peak at 48 hours (2 to 4 days) reaching about 1000 IU/L and then return gradually to normal from 8th to 14th day. * The predominant isoenzyme of LDH in cardiac muscle is LDH-1 (in Liver - LDH-5) * Albumin helps in distinguishing an acute liver disease from chronic liver disease.
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