The predominant isozyme of LDH in Lung is:: (A) LD-1, (B) LD-2, (C) LD-3, (D) LD-5
Answer is C. Isoenzymes of Lactate Dehydrogenase: Lactate dehydrogenase is a tetrameric enzyme and consists of four subunits. These subunits can occurs in two isoforms i.e. H isoform (for hea), M isoform (for muscle). LDH-1 (4H) - in the hea and RBCs LDH-2 (3H1M) - in the reticuloendothelial system LDH-3 (2H2M) - in the lungs LDH-4 (1H3M) - in the kidneys, placenta, and pancreas LDH-5 (4M) - in the liver and striated muscle Normal value of LDH in serum is 100-200 U/L. LDH level is 100 times more inside the RBC than in plasma, and therefore minor amount of hemolysis will result in a false positive test. Ref: Harper's Illustrated Biochemistry, 26th Edition, Page 57; Textbook of Biochemistry By Vasudevan, 5th Edition, Page 53