On the origin of mitochondria: a reexamination of the molecular structure and kinetic properties of pyruvate dehydrogenase complex from brewer''s yeast

45Ca2+ incorporated in response to glucose was selectively mobilized from the beta-cell-rich pancreatic islets of ob/ob-mice after raising the intracellular Na+ by removal of K+ or addition of ouabain or veratridine. Also studies of insulin release indicated opposite effects of glucose and Na+ on the intracellular sequestration of calcium. The fact that glucose inhibits insulin release induced by raised intracellular Na+ indicates that this sugar can lower the cytoplasmic [Ca2+]. The concept of a dual action of glucose on the cytoplasmic [Ca2+]. The concept of a dual action of glucose on the cytoplasmic [Ca2+] might well explain previous observations of an inhibitory component in the glucose action on the 45Ca2+ efflux.     

Identification of N- and C-terminal corticotropin peptides in the Mr 80000 form of neurophysin

The 125I-labeled Mr 80000 form of neurophysin has been purified from bovine neurohypophysi. Tryptic digests of this species were analyzed, prior to or after treatment with carboxypeptidase B, by high-pressure liquid chromatography followed by isoelectric focusing and the fragments compared with those generated by a similar treatment of reference bovine 1-39 adrenocorticotropin. The ACTH peptides 22-39 and 1-8, as well as the 1-7 derivative of the latter were identified by those two independent criteria. This provides chemical evidence supporting the hypothesis [8] that high Mr neurophysin may contain the sequence of ACTH.     

Solubilization and partial purification of protein kinase systems from brain membranes that phosphorylate calspectin: A spectrin-like calmodulin-binding protein (fodrin)

In brain tissue a spectrin-like calmodulin-binding protein calspectin, or fodrin, is concentrated in a synaptosome fraction, where most of the calspectin is associated with the synaptic membranes. This endogenous calspectin was phosphorylated by protein kinase system(s) associated with the membranes. Here, we report the solubilization and partial purification of the membrane-associated calspectin kinase activity. The activity was resolved on a gel filtration column into two fractions, peaks I and II having estimated M_r of 800 000 and 88 000. The activity of peak I was dependent on the presence of both Ca²⁺ and calmodulin. Peak II revealed a basal activity in the absence of Ca²⁺ and calmodulin, which was stimulated 2-fold by addition of Ca²⁺. Calmodulin had no effect on the peak II activity.     

Myosin light chain kinase binding to plastic

Methionine-81 and/or -8 of the transmembrane sialoglycoprotein, glycophorin A, have been specifically alkylated with ¹³CH₃I to produce the sulfonium ion derivatives [S-[¹³C]methylmethionine-8]glycophorin A and [S-[¹³C]methylmethionine-8 and -81]glycophorin A. ¹³C NMR spectra of these species show that the resonances of the methyl groups of the modified glycophorins occur at 26.1 ppm downfield from Me₄Si. A spin-lattice relaxation time of 0.4 was observed for the ¹³C-enriched methyl resonances of the sulfonium ion derivatives of Met-8 and -81, which corresponds to an effective correlation time of < 2× 10^?10 s. Demethylation of the 2 glycophorin A sulfonium ion species with 2-mercaptoethanol produces native glycophorin A which now has the ε-carbon of the methionine residue(s) 45% isotopically enriched. The ε-carbon of Met-8 was found to occur at 15.7 ppm downfield from Me₄Si whereas the ε-carbon of Met-81 exhibited an unusual chemical shift of 2.0 ppm downfield from Me₄Si. The spin-lattice relaxation time of both resonances was found to be ～0.3 s.     

Two forms of phosphoinositol kinase from germinating mung bean seeds

Phosphoinositol kinase, the key enzyme responsible for the biosynthesis of higher inositol phosphates has been isolated from the cotyledons of mung beans germinated for 24 hr and has been resolved into two different forms, phosphoinositol kinase A and phosphoinositol kinase B. Both forms were purified to homogeneity and characterized. The K_m values for ATP with phosphoinositol kinase A (1.78 × 10^?4 M) and phosphoinositol kinase B (3.12 × 10 ^?5 M) showed that phosphoinositol kinase B had a greater affinity for ATP. ATP could be partially replaced as phosphate donor by UTP and phosphoenolpyruvate in the case of phosphoinositol kinase A but not in the case of phosphoinositol kinase B.     

Phosphorylation of smooth muscle actin by the catalytic subunit of the cAMP-dependent protein kinase

Partially purified smooth muscle (chicken gizzard) actomyosin contains two major substrates of cAMP-dependent protein kinase: a protein of M_r = 130,000, identified as the calmodulin-dependent myosin light chain kinase, and a protein of M_r = 42,000. This latter protein was shown by a variety of electrophoretic procedures to be actin. Purified smooth muscle actin also was phosphorylated by the catalytic subunit of cAMP-dependent protein kinase. The rate of phosphorylation of smooth muscle actin was significantly enhanced by depolyjerization of actin. A maximum of 2.0 mol phosphate could be incorporated per mol G-actin. Skeletal muscle F-actin was not significantly phosphorylated by protein kinase; however, skeletal G-actin is a substrate for the protein kinase although its rate of phosphorylation was significantly slower than that of smooth muscle G-actin.