Glycogen phosphorylase from Neurospora crassa: purification of a high-specific-activity, non-phosphorylated form

The plastid phosphorylase as a multiple-role player in plant metabolism

The physiological roles of the plastidial phosphorylase in starch metabolism of higher plants have been debated for decades. While estimated physiological substrate levels favor a degradative role, genetic evidence indicates that the plastidial phosphorylase (Pho1) plays an essential role in starch initiation and maturation of the starch granule in developing rice grains. The plastidial enzyme contains a unique peptide domain, up to 82 residues in length depending on the plant species, not found in its cytosolic counterpart or glycogen phosphorylases. The role of this extra peptide domain is perplexing, as its complete removal does not significantly affect the in vitro catalytic or enzymatic regulatory properties of rice Pho1. This peptide domain may have a regulatory function as it contains potential phosphorylation sites and, in some plant Pho1s, a PEST motif, a substrate for proteasome-mediated degradation. We discuss the potential roles of Pho1 and its L80 domain in starch biosynthesis and photosynthesis.

Purification and properties of phosphorylase from Phymatotrichum omnivorum

The glycogen phosphorylase (EC 2.4.1.1) from the mycelium of Phymatotrichum omnivorum was purified by ammonium sulfate fractionation, gel filtration on Sephacryl S-200, and DEAE-cellulose ion-exchange chromatography to more than 100-fold. The purified enzyme was homogeneous; this was confirmed by polyacrylamide gel electrophoresis. Sodium dodecyl sulfate-gel electrophoresis indicated the relative molecular size of the enzyme was around 145,000. The approximate molecular weight by gel filtration was 116,000. The optimum pH of the enzyme was 7.0 and the enzyme was more specific for glycogen, with a Km value of 0.36 mg/ml. Nucleotides AMP, ADP, and ATP and compounds containing an "SH" group inhibited the enzyme activity. Diethyldithiocarbamate, EDTA, ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid, and Cu2+ were the potent inhibitors of the glycogen phosphorylase activity, Ca2+, Cu2+, Co2+, and Fe2+ stimulated the enzyme activity. The enzyme preparation was stable at 4 degrees C during a period of 30 days.

Effect of glucose on alpha-glucan degradation in Polyporus circinatus

The effect of glucose on the enzymes involved in the degradation of a reserve alpha-glucan in Polyporus circinatus was studied. The levels of phosphorylase activity, endoamylase, amylo-1,6-glucosidase were regulated by glucose concentration.