Extractable and Residual Glycogen in Tissues of the Rat

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Abstract
Carbohyrate remaining in the residues left after extraction of the liver and muscles of normal rats with 10% trichloroacetic acid (TCA) was largely freed from the protein by digestion in hot concentrated alkali. It was then soluble in water and in TCA, precipitable with ethanol, completely hydrolyzable to fermentable reducing substances, and susceptible to amylase. Extraction of muscle, heart, or liver of rats with other protein precipitants (tungstic, metaphosphoric or sulfosalicylic acids), or boiling followed by adjustment to pH 5, yielded the same amounts of glycogen as extraction with TCA, whereas extraction with hot or cold water or with dilute mineral acid or alkali yielded much larger proprtions of the glycogen present. Part of the native glycogen thus appeared to be associated with the tissue proteins in some moderately firm combination. Parallel estimations of the TCA-extractable, total, and residual glycogen in the heart, gastrocnemius muscle, liver, and diaphragm of 150 rats in a variety of conditions indicated that the proportions of the 2 fractions varied in different organs and with the state of the animals. The extractable glycogen was the principal variable moiety in all of the tissues examined, the residual or bound glycogen remaining relatively constant through wide ranges of total glycogen concentrations; but the latter fraction was also susceptible to alteration under some conditions.