Regulation of Artemia Glycogen Phosphorylase: Effect of Diguanosine Nucleotides
Dormant cysts of Artemia contain glycogen phosphorylase, a key enzyme in the utilization of energy reserves at resumption of metabolic activity. The enzyme is regulated through a phosphorylation/dephosphorylation mechanism similar to that operating in other higher organisms. This mechanism of interconversion is active during development and the relative ratio of the two forms changes significantly in the period preceding the emergence of the nauplius.
The enzyme was purified to homogeneity by a procedure involving ion-exchange and gel filtration chromatography and an affinity chromatography step on AMP-Sepharose.
Preliminary attempts to crystallize the protein were not successful due to difficulties in obtaining other than submicroscopic crystals.
The kinetic properties of the purified enzyme were determined. The activity is stimulated by AMP and is inhibited by diguanosine tetraphosphate (Gp4G) one of the 5−5′ dinucleoside polyphosphates present in large amounts in Artemia cysts.
Diguanosine triphosphate (Gp3G) does not inhibit phosphorylase activity appreciably in vitro. The presence of these nucleotides at the first stages of development and their rapid degradation may contribute to the regulatory system affecting overall glycogen phosphorylase activity.