貝類のグリコーゲンの構造および代謝に関する研究

抄録

The size and the shape of shellfish glycogen particles varied with the extraction procedure. Glycogen particles prepared by the dimethyl sulfoxide (DMSO) extraction method were relatively large in size and showed a rosette-like structure (large particle, α-particle) composed of several small particles (β-particle), whereas glycogen extracted with trichloroacetic acid (TCA) and commercial glycogen prepared by extraction with barium hydroxide containing zinc sulfate showed much smaller particle size. The latter preparations did not have a rosette-like structure and they were more susceptible to pullulanase. Treatment with acids, such as TCA and phosphotungstic acid, reduced the size of particles significantly but, on the other hand, the particles were rather resistant to alkalis, such as 0.1M or 0.5M sodium hydroxide. The large particles were not dissociated into small particles on treatment with 2-mercaptoethanol, or on protease or β-amylase treatment. Short time exposure of the large particles to a high concentration of α-amylase caused some degradation, yielding small particles. These results suggest that each large glycogen particle is composed of several small particles, which are linked to each other through an α-1, 4-glucan chain.
There are two forms of glycogen phosphorylase in oyster adductor muscle, namely, an AMP-independent form (phosphorylase a) and an AMP-dependent form (phosphorylase b). Purified phosphorylase a was not inhibited by ATP or glucose-6-P in the presence of AMP, while phosphorylase b was strongly inhibited by ATP and glucose-6-P. Unlike in the case of mammalian phosphorylases, it was shown that in the oyster adductor muscle, phosphorylase b was regulated by the concentrations of glucose-6-P and ATP, and the rate of conversion from the b form to the a form was very low. Only the AMP-dependent form (phosphorylase b) was found in scallop adductor muscle. The purified phosphorylase b from the scallop adductor muscle showed strong affinity to AMP (Km for AMP, 17.4μM). It was shown that in the scallop adductor muscle, the activation of the phosphorylase was not caused by conversion from the b form to the a form, but by the increase in AMP concentration.