Regulation of Starch Synthesis

Plant ADP-Glucose Pyrophosphorylase -Recent Advances and Biotechnological Perspectives (A Review)

“…These conclusions were drawn from studies on a irreversible binding of labelled pyridoxal-P (ana log of PGA) and 8-azido-ADP-glucose (analog of ADP-glucose) to the purified spinach enzyme [13,14,27], and from the comparison of conserved re gions of AGP from several species [17,28,29], Based on studies with spinach AGP, the activatorbinding site was postulated to be located both on the small and large subunit [13,27], while the substrate-binding site is present almost exclusively on the large subunit [27]. However, an Arabidopsis m utant entirely lacking the large subunit o f AGP and having only about 4% of the small subunit protein has been reported [5] to have about 5% of the AGP activity, when compared to wild type plants, suggesting that the small subunit o f A G P in this species does contain the substrate-binding do main.…”

“…Unfortunately, the state of oligomerization of the small subunits of native A G P in this Arabi dopsis m utant is unknown at present. The hom o tetrameric AGP from E. coli differs from plant A G P in the structure of the activator-binding site, but not the substrate-binding dom ain [14,[27][28][29], probably reflecting the distinct nature of activa tors of the bacterial and plant AGP.…”

“…Tissue-specific transcripts for A G P have been identified and sequenced from several species ( Table I). The identification of cDNAs coding for AGP was accomplished by screening expression libraries with the antibodies against either spinach [17,27,28] or potato AGP [24], by hybridization to cD NA probes [17,29,30] and, most recently, by polymerase chain reaction technique, using oligo nucleotide primers based on conserved regions of the cDNAs (P. Villand, unpublished). The latter technique seems especially promising, since it al lows a direct amplification o f transcripts and ge nomic sequences, opening new opportunities for the characterization of the structure and expres sion of different homologous genes of AGP.…”

“…The degree o f identity o f the rice en dosperm small subunit o f A G P [28,29] to the c o r responding proteins from p o ta to tubers [25], maize endosperm [30], spinach leaves [27] and barley en dosperm [Villand, unpublished] is 88, 89, 76 and 91% , respectively. The nucleotide sequences are less conserved (e.g.…”