The effects of nonsuppressible insulin-like protein (NSILP) on cyclic nucleotide metabolism in rat liver.

Nonsuppressible insulin-like protein (NSILP), 100 ng/ml, inhibited cyclic AMP accumulation in rat liver, as stimulated by glucagon, 10^?7M, from 493 ± 12 to 183 ± 7 pmoles/gm tissue (p<0.001), but did not alter basal levels of cyclic AMP, 143 ± 2 pmoles/gm tissue. NSILP, 100 ng/ml, also inhibited cyclic AMP accumulation, stimulated by epinephrine, 5 × 10^?4M, from 387 ± 12 to 233 ± 9 pmoles/gm tissue. With 1 μM as substrate, NSILP, 100 ng/ml, increased cAMP-dependent phosphodiesterase activity in liver slices from 19.08 ± 0.18 to 24.94 ± 0.38 pmoles cAMP hydrolyzed/mg protein/min (p<0.001), but did not alter this enzyme activity in broken cell preparations of rat liver. Cyclic GMP levels in liver slices, 22.5 ± 0.3 pmoles/gm tissue, were increased by NSILP to 36.3 ± 0.5 pmoles/gm tissue (p<0.01). NSILP had no effect on adenylate cyclase activity. These changes, caused by NSILP in cyclic nucleotide metabolism in liver, resemble those described for insulin, and suggest that alterations in cyclic nucleotide levels in liver may be relevant to other hepatic effects of NSILP.     

Separation of two HMM-S1 species from white muscle myosin

Heavy meromyosin subfragment 1 was resolved by chromatography on DEAE-cellulose into two fractions characterized by the nature of the alkali light chains present. It was shown that even in an HMM-S1 preparation with an extensive fragmentation of the heavy chain a polyacrylamide gel electrophoresis analysis differentiates alkali light chains among the light fragmentation components. A non-fragmented HMM-S1 was obtained from a papain digest of myofibrils and the chromatographic analysis supplied further evidence of the separation of the two species of HMM-S1 present in rabbit white muscle myosin.     

Inhibitory effect of hydroxyurea on [3-H]leucine incorporation in human peripheral lymphocytes.

Hydroxyurea (HU), generally considered to be a specific inhibiter of DNA synthesis, has an inhibitory effect on the incorporation of TCA-precipitable [3-H]leucine in peripheral lymphocytes. This action is not secondary to the inhibition of DNA synthesis since incorporation of [3-H]leucine is unaffected when DNA synthesis is inhibited by 5-fluorodeoxyuridine (FUdR); it does not appear to be directly related to inhibition of RNA synthesis; and it is not mediated at the level of translation since HU has no effect on protein synthesis in rabbit reticulocytes. The relevance of these findings to the use of HU as a DNA inhibitor is discussed.     

Resolution of cyclic AMP stimulated protein kinase from polymerization-purified brain microtubules.

Polymerization-deploymerization purified microtubules from mouse brain contain, in addition to tubulin, several minor proteins, including protein kinase activity. The protein kinase copurifies with microtubules in constant proportion to tubulin through two, three, or four cycles of polymerization; it can be resolved from tubulin by gel filtration chromatography and has an apparent molecular weight of 280,000. Its activity is stimulated 7-fold by cyclic AMP, and resembles the soluble brain protein kinase described by Miyamoto $\text{et al.}$ (1). The microtubule preparation serves as an endogenous substrate for this protein kinase; both 6S and 30S tubulin are substrates for phosphorylation to the extent of about 0.10 ± 0.05 moles/mole.