Abstract
We have studied the structure of myosin heavy chain (MHC) in the pectoralis muscle of genetically dystrophic (Connecticut Strain) and White Leghorn chicks. MHC was alkylated with N-ethylmaleimide, purified by Sepharose-4B chromatography, and cleaved with cyanogen bromide. The MHC CNBr peptides were analyzed by one-dimensional and two-dimensional isoelectric focusing/sodium dodecyl sulfate gradient gels and by amino acid sequencing. Specific changes were detected in the gel patterns which could be correlated with the loss of muscle function as measured by the exhaustion score (the ability of chicks to rise from a reclining position) in three experimental groups (exhaustion scores: less than 3, 10-20, greater than 30). We have also examined the amino acid sequence of a 3-methyl-histidine-containing peptide which originates from the 20-kDa fragment of pectoralis muscle MHC in dystrophic chicks: Val-Leu-Asn-Ala-Ser-Ala-Ile-Pro-Glu-Gly-*Gln-Phe-*Ile-Asp-Ser-Lys-Lys- Ala-Ser-Leu-Gln-Lys-Leu-Gly-Ser-Ile-Asp-Val-(Asp, 3-methylhistidine, Gln). Comparison of the homologous MHC sequences shows two positions at which MHC from dystrophic chicks differs from that of the White Leghorn chicks *(Glu----Gln and Met----Ile). Thus, both the peptide map and sequence analyses demonstrate that in avian muscular dystrophy an abnormal pectoralis MHC is synthesized. It is not yet clear whether the "dystrophic" MHC is a variant MHC or if it arises from the abnormal expression of an earlier developmental form (embryonic or neonatal) of pectoralis muscle MHC.
Highlights
We have studied thsetructure of myosin heavy chain with the unusual methylated amino acid, 3-methylhistidine, (MHC) inthepectoralis muscle of genetically dys- in rabbit skeletal muscle and of the homologous peptides in trophic (Connecticut Straina)nd White Leghorn bovine and rabbit hearts andin skeletal muscle of developing chicks
Specific changes were detected inthe gel patterns which could be correlated with theloss of muscle function as measured by the exhaustion score(the ability of chicks to rise from a reclining position) in three experimental
Avian muscular dystrophy is inherited as a simple autosomal recessive trait [28, 29]
Summary
The data from one-dimensional gradient gels led us to conclude that CNBr digests of pectoralis MHC of the H, L, and D groups yield peptide mixtures with different electrophoretic patterns. The differences maybe assigned into two retic analysis of partial proteolytic digests revealed a different subgroups; first, peptides which arepresent in the CNBr MHC digestion pattern in the pectoralis muscle of dystrophic digest of the H group, but fainter or not present in the L animals as compared to the White Leghorn controls [7]. The 3-methylhistidine content of the fractions was dimensional gel maps of the CNBr peptides; ( b ) amino acid determined by amino acid analysis, and the fractions most sequence changes in homologous 3-methylhistidine peptides; enriched in 3-methylhistidine were collected and further pu- and ( c ) the appearance of a new type of MHC sequence in rified on Dowex 50 (elution pattern not shown).
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