Which isoenzyme has maximum electrophoretic mobility:
**Core Concept**
Isoenzymes, also known as isozymes, are different molecular forms of an enzyme that catalyze the same chemical reaction but differ in their amino acid sequence and, consequently, their physical and chemical properties. In the context of lactate dehydrogenase (LDH), isoenzymes are classified into five main types based on their electrophoretic mobility, with LDH-1 being the most anodal (having the highest electrophoretic mobility) and LDH-5 being the most cathodal (having the lowest electrophoretic mobility).
**Why the Correct Answer is Right**
The correct answer is LDH-1 because it contains the M-subunits, which are smaller and have a higher negative charge than the H-subunits. This results in LDH-1 having a higher electrophoretic mobility, allowing it to migrate more quickly towards the anode during electrophoresis. The M-subunits are encoded by the LDHB gene, while the H-subunits are encoded by the LDHA gene.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because LDH-2, which contains two M-subunits and two H-subunits, has a lower electrophoretic mobility than LDH-1 due to its higher molecular weight.
**Option B:** This option is incorrect because LDH-3, which contains one M-subunit and three H-subunits, has an intermediate electrophoretic mobility between LDH-1 and LDH-2.
**Option C:** This option is incorrect because LDH-4, which contains three M-subunits and one H-subunit, has a lower electrophoretic mobility than LDH-3 due to its higher molecular weight.
**Option D:** This option is incorrect because LDH-5, which contains four M-subunits, has the lowest electrophoretic mobility among all the isoenzymes due to its high molecular weight.
**Clinical Pearl / High-Yield Fact**
In clinical practice, the ratio of LDH isoenzymes can be used to differentiate between myocardial infarction and skeletal muscle injury. Myocardial infarction typically results in an elevation of LDH-1 and LDH-2, while skeletal muscle injury results in an elevation of LDH-2 and LDH-3.
**Correct Answer:** A. LDH-1.