Cyclic GMP-dependent protein kinase, purified to homogeneity from bovine lung, was shown to activate hormone-sensitive lipase partially purified from chicken adipose tissue. The degree of activation was the same as that effected by cyclic AMP-dependent protein kinase although higher concentrations of the cyclic GMP-dependent enzyme were required (relative activities expressed in terms of histone H2b phosphorylation units). Activation by cyclic AMP-dependent protein kinase was completely blocked by the heat-stable protein kinase inhibitor protein from skeletal muscle but activation by the cyclic GMP enzyme was not inhibited. Lipase fully activated by cyclic AMP-dependent protein kinase showed no further change in activity when treated with cyclic GMP-dependent protein kinase. Lipase activated by cyclic GMP-dependent protein kinase was reversibly deactivated by purified phosphorylase phosphatase (from bovine heart); full activity was restored by reincubation with cyclic GMP and cyclic GMPdependent protein kinase. Cholesterol esterase activity in the chicken adipose tissue fraction, previously shown to be activated along with the triglyceride lipase by cyclic AMP-dependent protein kinase, was also activated by cyclic GMP-dependent protein kinase. Crude preparations of hormone-sensitive triglyceride lipase from human or rat adipose tissue and cholesterol esterase from rat adrenal were also activated by cyclic GMP-dependent protein kinase. Purified hosphorylase kinase (rabbit skeletal muscle) was also shown to be activated by cyclic GMP-dependent protein kinase. The present results, together with those of other workers on histone phosphorylation, suggest that the substrate specificities of cyclic GMP-dependent and cyclic AMP-dependent protein kinase may be similar. This is discussed in the light of a model recently proposed with regard to the relationship between the subunit structures of the two kinases. The physiologic significance of the findings remains to be established.
Lateral cordless fragments isolated from the postpharyngeal section of Dugesia dorotocephala formed a large normal head at a 90" angle to the original antero-posterior polarity; postcerebrally, only a hump of undifferentiated tissue developed. This "head-hump'' pattern, and also other types observed in previous studies of lateral fragments, were attributed to the absence of the nerve cord. In order to confirm the inductive role of the nerve cord and to eliminate the possibility that the "head-hump syndrome" was due to the relative proportions of other tissues besides nerve, body fragments of two experimental groups were observed: (1) the five types of fragments which had no nerve cord but had varying proportions of other tissues present formed primarily "head-hump" types of regenerates.(2) Almost all fragments which had varying amounts of nerve cord present but the same proportions of other tissues formed regenerates of normal body proportions. Therefore, the absence of the nerve cord does determine the "head-hump syndrome."Isolated postpharyngeal half segments containing one nerve cord were allowed to regenerate for varying periods of time before the lateral cordless fragment was isolated. The number of "head-hump'' regenerates from lateral fragments isolated after a one-day or longer contact with the nerve cord gradually decreased, and the number of regenerates with incomplete head development or which were more elongated postcerebrally increased. These results indicate that the nerve cord acts gradually to determine the differentiation of specific tissues rather than rapidly to determine the overall body plan.
The messenger RNA (mRNA) for avidin, which represents less than 0.05% of the total cellular proteins, was partially purified from hen oviduct, and the presence of avidin mRNA was shown to depend upon prior stimulation by progesterone. A total nucleic acid extract was subjected to oligo (dT)-cellulose chromatography, followed by Sepharose 4B chromatography, preparative agarose gel electrophoresis, and sucrose gradient centrifugation. The relative purity of each preparation was assessed by translation in a wheat-germ system; avidin messenger RNA activity was measured by specific immunoprecipitation of synthesized proteins. Avidin mRNA was separated from the bulk of the total messenger RNA activity of the oviduct and from all ribosomal RNAs to produce greater than a 1000-fold enrichment of avidin mRNA activity compared with total cellular RNA. Based on the translation assay, the most highly purified fraction contained about 2.5% avidin messenger RNA. Avidin mRNA activity was absent in partially purified mRNA obtained from estrogen-stimulated chick oviducts, but was detected in oviducts following progesterone administration.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.