Certain Physico-Chemical Characteristics of Muscle Globulin.

Abstract

The significance of the protein constituents of muscle for the contractile process has long been recognized. The instability of these bodies, however, has rendered difficult their characterization. Danilewsky described the extraction of muscle protein with sal ammoniac in 1881. The older method of expression, despite rigid precautions, often led to “denaturation” or “clotting of muscle plasma.” The properties of muscle globulin, as of other globulins, are altered both by too low salinity and by too high acidity. Howe has employed phosphate buffers as solvents to overcome these difficulties. In the present investigation an ammonium chloride solution, rendered alkaline by excess of ammonia, was used as solvent and yielded solutions of muscle protein which, for several months, retained solubility in neutral salt solutions. A globulin-like fraction of ox muscle protein was studied, which presumably corresponded to the “myosin” of von Fürth and the “paramyosinogen” of Halliburton. The method of preparation depended upon: (a) its low solubility in water or dilute salt solution; (b) its greater solubility in the presence of higher concentrations of neutral salt; (c) its precipitation from solutions less than half-saturated with respect to ammonium sulfate. Fresh muscle was finely ground and stirred into a two-molal ammonium chloride solution, to which ammonium hydroxide was slowly added to a concentration one-third normal. This ammonia buffered the acid products and thus prevented “denaturation.” The dissolved protein, after centrifugation and filtration, was alternately precipitated by ammonium sulfate, dissolved in more dilute salt solution, and precipitated by further dilution. The reaction was always maintained between pH 8.0 and 8.5 by ammonia. Precipitated by ammonium sulfate, the muscle globulin was freed from albumins and hemoglobin; precipitated by dilution from the serum globulins which dissolve in more dilute salt solutions.