A recent renewal of interest in the muscle extractives carnosine (fi-alanylhistidine) and anserine" (&alanyl-l-methylhistidine) , their component imidazoyl amino acid,, q as well as 3-methylhistidine and the dipeptide homocarnosine (y-aminobutyrylhistidine) , may be noted (l-4). The present paper deals with the determination of these dipeptides and the free imidazoyl amino acids in muscle. The muscle is finely minced with scissors and transferred to a microhomogenizer for more complete disintegration.
The colloidal mixt'ure is extracted three times with small portions of boiling water and the extracts passed through a glass wool filter. Removal of the proteins by trichloroacetic acid or sulfosalicyclic acid at a final concentration of 3% yields clear filtrates which can be applied directly to the resin columns of the amino acid analyzer for separation and quantitation.
Filtrates obtained by both methods of deproteinization yield nearly identical values for the peptides and amino acids under consideration. If the analysis is not to be done promptly after deproteinization the filtrates should be kept in a frozen state.
Breast muscle of pigeons, various muscles of rats and man, and leg muscles of monkeys have been analyzed. The muscle samples from monkeys were obtained by biopsy, the human samples from autopsy material and from various muscles made available during surgical procedures. Amounts from 22 to 200 mg of muscle have been used but whenever possible the filtrate put on the resin column should contain the equivalent of 40 to 70 mg of muscle in 1, 2, or 3 ml. Since the