Progress in the understanding of glycogen biogenesis in rat heart.

The sequence of glucosylation steps from "genesine", the naked initiation protein, to rat heart glycogen are described. During a pulse experiment with UDP-14C-glucose the radiolabelled 14C-glucosylated protein band of 38 and 42 kDa appeared first. Mn+2 stimulates the first transfer of glucoses to "genesine" and the 38 kDa and 42 kDa protein bands appear. Although further growth is inhibited by Mn+2, this inhibition is reversed by PMSF+Glc6P. In the absence of Mn+2, a major 14C-glucosylated protein band of 60 kDa and also a faint one in the location of 42 kDa appeared. Designing the synthetic and degradative processes it is possible to go from the 42 kDa 14C-glucosylated protein band through species of higher mw to glycogen and back to the 42 kDa one. In the "genesine" autoglucosylating process involved in the initiation of rat heart biogenesis, several dissimilar activities had to be distinguished. The first glycogen initiator 1 (GI1) is that with an activity stimulated by Mn+2 which transfers one or two glucoses. The other glycogen initiator 2 (GI2) is inhibited by Mn+2 and in its absence produces a glucosylated protein band of 60 kDa. Finally a third one, stimulated by Glc6P, we named it Elongator 1 (E1), which in the presence of mumolar concentration of UDPGlc originates a family of glucosylated protein bands almost from 42 kDa to 200 kDa.