CHARACTERIZATION OF THE MYOSIN HEAVY-CHAINS OF AVIAN ADULT FAST MUSCLES AT THE PROTEIN AND MESSENGER-RNA LEVELS

High resolution anion-exchange chromatography of myosin subfragment-l in avian fast muscles revealed five fast heavy chains (I-V) expressed in muscle-specific patterns. Sequence analysis of a unique peptide est ablished that the proteins differed in primary structure and suggested correlation with heavy chain genes identified independently by Robbin s and coworkers. The identities of the isoforms and their expression p atterns were confirmed at the mRNA level by a reverse-transcription, 5 '-anchored PCR procedure. The fast white pectoralis major muscle posse ssed heavy chain I, the posterior latissimus dorsi muscle, of similar fibre type, expressed heavy chains I, III and IV. The fast red adducto r superficialis muscle expressed either, or both, of heavy chains II a nd IV. The lateral gastocnemius muscle, of mixed fibre type, expressed heavy chains II-V. In general, heavy chains I, III and V appeared to be favoured in fast white fibres, while heavy chains II and TV were ch aracteristic of fast red fibres. These results imply a greater subtlet y of fast muscle function than has previously been appreciated.