Lactate dehydrogenase (LD) measurements are described as what kind of unit related to its subunit composition?

• A. Tetrapeptide / 4 units (H and M subunits)
• B. Dimeric units
• C. Monomeric unit
• D. Hexameric complex

Answer: (A)

Lactate dehydrogenase is a tetrameric enzyme, meaning its active form is assembled from four subunits. In humans, these subunits are of two types: heart (H) and muscle (M). The different LDH isoenzymes arise from various combinations of these four subunits within the tetramer, so measurements and descriptions of LD units refer to this four-subunit, tetrameric complex. That’s why describing the unit as a four-subunit (tetrameric) assembly fits best. The ideas of a dimer (two subunits), a monomer (one), or a hexamer (six) don’t match LDH’s known structure.