Free and fixed glycogen in rat muscle

Proglycogen and macroglycogen: artifacts of glycogen extraction?

“…3). These findings corroborate those of the many studies performed mainly in the 1950s that have reported that in response to conditions affecting muscle glycogen levels such as insulin administration, electrical stimulation, adrenaline injection, hyperthyroidism, or death, there is a preferential or even exclusive change in the level of acid-soluble glycogen [2][3][4][5]20,38]. In contrast, studies using the homogenization-free glycogen extraction protocol of Adamo and Graham [13] have reported that it is the acid-insoluble glycogen that accounts for most of the changes in total glycogen concentration when the levels of total glycogen are low, whereas the absolute contribution of the acid-soluble glycogen is relatively more important when total glycogen levels are elevated [13,[15][16][17][18]22].…”

“…Our results show that for the optimal extraction of acid-soluble glycogen, 1 minute of homogenization is required using a Janke and Kunkel UltraTurrax T-25 homogenizer, and the acid-insoluble fraction must be reextracted at least 3 times to recover 97% of acidsoluble glycogen. Under these circumstances, the proportion of acid-soluble glycogen in muscles of fed rats ranges between 52% and 64%, a finding similar to those of the recent [14,20] and earlier studies that have included a homogenization step in their extraction protocols [2][3][4][5][6][7]. In contrast, when glycogen is extracted without a homogenization step, as described by Adamo and Graham [13], our results show that acid-insoluble glycogen is heavily contaminated with acid-soluble glycogen, with only 16% of glycogen found in the acid-soluble fraction.…”

“…One indirect approach to determine whether acid-soluble and acid-insoluble glycogens represent physiologically distinct glycogen pools is to examine their patterns of response to a physiological challenge that causes a marked change in muscle glycogen levels [2][3][4][5][6][7][15][16][17][18]11,12,22], such as the fasting-to-fed transition. Because muscle fiber composition has the potential to affect our results, the patterns of change in acid-soluble and acid-insoluble glycogen species to refeeding after a fast were examined in muscles of different fiber compositions.…”

“…Although the mechanism underlying the existence of these pools has remained elusive for several years, this has not prevented a substantial volume of research from being undertaken mainly in the 1950s to elucidate the responses of these glycogen pools to a broad range of physiological conditions [2][3][4][5][6][7]. It was only in the early 1990s that the basis for the variations in acid solubility of different glycogen fractions was alleged to have been explained at the molecular level.…”

Brain Glycogen Structure and Its Associated Proteins: Past, Present and Future

“…When the TCA extraction method was first introduced for the purification of glycogen, it was observed that a portion of the glycogen was resistant to extraction by cold TCA (Willstätter and Rohdewald 1934). It could not be released unless the tissue was treated with heat, alkali, or protease, so it was concluded that this resistant fraction was attached to protein, and the two fractions were called lyo-("free") and desmo-("fixed") glycogen (Willstätter and Rohdewald 1934;Van Heijningen and Kemp 1955). Such observations also gave rise to the terms acid-soluble, i.e.…”