Comparison of the amino acid composition of the intracellular and extracellular matrix protein fractions isolated from avian skeletal muscles.

Intracellular and extracellular skeletal muscle protein fractions were isolated from the legs and breasts of young and adult White Leghorn chickens and quantified by detailed amino acid analysis. This involved repeated homogenization in the presence of 50 mM CaCl2, neutral phosphate-buffered saline (pH 7.4), solubilization by 2% sodium dodecyl sulfate (SDS), and centrifugation to separate all intracellular muscle proteins from the extracellular matrix. The total SDS-soluble intracellular muscle proteins in the adult and young birds ranged respectively from 93.2 to 94.5% in the leg and from 93.5 to 94.1% in the breast muscles. Collagen and collagen-like proteins in the extracellular matrix protein fractions were calculated from the amounts of 5-hydroxylysine found in their 96-h acid hydrolysates and elastin content from the amounts of desmosine present. Total collagen ranged from 3.42 to 5.18% in legs and from 2.91 to 3.89% in breasts. The elastin content of leg muscles represents only .061% of the total muscle protein. The calculated protein efficiency ratios for intracellular avian muscle proteins averaged 3.2 compared with a mean value of 1.4 for the extracellular matrix.