ISSN:
1432-136X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary In a previous paper, two types of cyclic nucleotide-dependent protein kinases, namely cGMP dependent “G-kinase” and cAMP dependent “A-kinase”, in silkworm eggs has been reported (Takahashi et al. 1975; Takahashi 1976). One of these, G-kinase, has now been purified 2400-fold by means of ammonium sulfate fractionation, chromatography on hydroxylapatite, DEAE cellulose, and gel filtration. Some of the properties of the enzyme are described. The enzyme is highly dependent on cGMP; it is strongly inhibited by GTP in a noncompetitive manner not only for ATP but also for cGMP. GTP was found to be highly inhibitory on G-kinases from various tissues of the silkworm, but did not inhibit the A-kinase. Incubation of the egg extract with [γ-32P]ATP and Mg2+ led to the formation of three major32P-labelled proteins, with molecular weights of 42.000, 70.000 and 180.000 as analyzed by SDS polyacrylamide gel electrophoresis. Two of them corresponded to the subunits of vitellin. The silkworm vitellin was effectively phosphorylated both by the highly purified G-kinase and by the A-kinase. It is concluded that the G-kinase is involved in the phosphorylation of vitellin in developing silkworm eggs.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00694583
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