The expression of myosin light chains and tropomyosin in human muscle biopsies with histochemical type 1 and type 2 fiber deficiency

Two‐dimensional gel electrophoresis (2DE) was used to compare the protein composition of human muscle biopsies that were shown by histochemical staining to be deficient in either type 1 or type 2 fibers. Distinct quantitative differences were found in the myofibrillar protein composition of muscle from a 43‐year‐old woman with proximal limb weakness that showed almost total absence of type 1 fibers and muscle from a 2.5‐year‐ girl with congenital myopathy in which there was severe lack of type 2 fibers. These data indicate that human type 1 and type 2 muscle fibers express distinct isoforms of myosin light chains and α‐tropomyosin.