Myofibrillar proteins in white muscle of the developing African catfish Heterobranchus longifilis (Siluriforms, Clariidae)

Developmental changes in myofibrillar protein composition were investigated in the myotomal muscle of the African catfish, Heterobranchus longifilis ( Clariidae), by several electrophoretic techniques. The main muscle fibres o f larvae and the fast-white muscle fibres of juvenile and adult fish were f ound to express distinct myosin heavy chain and myosin light chain 2 (LC2) isoforms. Three myosin LC2 chains were successively detected, differing by their isoelectric points. In contrast, the alkali light chains remained qua litatively and quantitatively unchanged during fish growth. Actin, alpha-tr opomyosin, and troponin-C (TN-C) were also similar in larval, juvenile, and adult white muscle, but an additional larval tropomyosin isoform was found in the first developmental stages. Two isoforms of troponin-T (TN-T) and t roponin-I (TN-I) were synthesised in the course of fish growth. Transition from the larval to the adult isoform was much faster for TN-T than for TN-I . Slow-red muscle myofibrils from adult H. longifilis showed no common comp onent (except actin) with larval, juvenile, or adult fast-white muscle myof ibrils. Red myofibrils displayed a single TN-T and a single TN-I isoform, b ut two isoforms of TN-C. The myofibrillar protein isoforms synthesised at a ny given developmental stage almost certainly reflect changes in the functi onal requirements of swimming muscles in the course of fish development.