Protein phosphorylation during Rhodnius prolixus embryogenesis: protein kinase casein kinase II activity

Protein kinase casein kinase II (CK II) activity was assayed during Rhodnius prolixus embryogenesis. Vitellin (VT) is the main endogenous substrate during the whole development. It is maximally phosphorylated at the third day of embryogenesis by CK II and then its phosphorylation decreases to a basal level by the time of first instar eclosion. When dephosphorylated casein was used as an exogenous substrate a different profile of enzyme activity was obtained. CK II activity increases on day 1 after fertilization and reaches a plateau on day 7 and its activity remains elevated until eclosion. Extracts obtained from oocytes or from 3-day old eggs were fractionate through gel filtration chromatography. CK II activity was assayed in each fraction and the enzyme obtained from the 3-day old eggs was shown to be three times more active than that obtained from oocytes, although the amount of enzyme present in the fractions was the same. These enriched CK II fractions were assayed against different effectors, such as: cAMP, H-8, H-89, calphostin C, sphingosine, polylysine and heparin. Heparin was the most effective one. When CK II activity was assayed in non-fertilized eggs, no activation of the enzyme was observed when compared to fertilized eggs. These data indicate that CK II is activated in a fertilization dependent process. The decrease in CK II activity against VT coincides with the beginning of VT proteolysis processing suggesting a possible relationship between protein phosphorylation and yolk degradation.