Distribution of LDH Isozymes in Human Skeletal Muscle

Abstract

LDH isozyme patterns in human skeletal muscle have been studied in 17 subjects of both sexes and varying age groups (16–55 years). Homogenized muscle biopsy materials have been analysed for total LDH activity (V_max) in both directions, as well as enzyme activity attributable to isozymes. In addition, different isozymes have been electrophoretically separated and stained. In human skeletal muscle all (5) LDH isozymes were present, although the relative contribution from the more heart-specific isozymes (LDH 1 plus 2) declined the higher the total LDH activity. In absolute terms, however, this decline corresponded to a 2 to 3 fold increase in the activity of LDH 1 plus 2 when the two extremes with low and high total LDH activity, respectively, were compared. Per cent LDH 1 plus 2 of total LDH activity was found to increase with an increase in per cent slow-twitch fibres. As an increase in total LDH activity was synonymous to an increase in per cent fast-twitch fibres, it was concluded that LDH isozyme pattern in human skeletal muscle was related to the fibre type. Moreover, the slow-twitch fibre had a relatively higher activity of the isozyme fractions corresponding to the more heart-specific isozymes LDH 1 and LDH 2.

Key Words:

• Fibre composition
• human skeletal muscle
• LDH
• LDH isozymes lactate metabolism
• muscle enzymes