As with other human tissues isoenzymes can be demonstrated in the human epidermis. In the absence of substrate, nonspecific reduction of oxidized nicotine adenine dinucleotide (NAD) but not of nicotine adenine dinucleotide phosphate (NADP) occurs. The three bands which result are identical in migration with bands M4, M3H1, and M2H2 of lactic dehydrogenase (LDH) but are much weaker than the bands found when lactate is included as a substrate. Bands M1H3 and H4 of LDH can also be demonstrated in human epidermis although in lesser amounts. In addition at least two isoenzymes of malic dehydrogenase (MDH), three of isocitric dehydrogenase (ICDH), and two of glucose-6-phosphate dehydrogenase (G6PDH) can be demonstrated. Two quite distinct polyphenoloxidases have been demonstrated in both white and Negro epidermis. The functional significance of these isoenzymes remains to be determined.
Ohkawara A, Halprin J, Barber P, Halprin KM. Human Epidermal Isoenzymes. Arch Dermatol. 1967;95(4):412-415. doi:10.1001/archderm.1967.01600340072017