The Journal of biological chemistry
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The complete amino acid sequence of human salivary statherin, a peptide which strongly inhibits precipitation from supersaturated calcium phosphate solutions, and therefore stabilizes supersaturated saliva, has been determined. The NH2-terminal half of this Mr=5380 (43 amino acids) polypeptide was determined by automated Edman degradations (liquid phase) on native statherin. The peptide was digested separately with trypsin, chymotrypsin, and Staphylococcus aureus protease, and the resulting peptides were purified by gel filtration. ⋯ The NH2-terminal one-third is highly polar and includes three polar dipeptides: H2PO3-Ser-Ser-H2PO3-Arg-Arg-, and Glu-Glu-. The COOH-terminal two-thirds of the molecule is hydrophobic, containing several repeating dipeptides: four of -Gn-Pro-, three of -Tyr-Gln-, two of -Gly-Tyr-, two of-Gln-Tyr-, and two of the tetrapeptide sequence -Pro-Tyr-Gln-Pro-. Unusual cleavage sites in the statherin sequence obtained with chymotrypsin and S. aureus protease were also noted.
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Hypophysectomy of adult rats results in approximately a 50% decrease in the rate of albumin synthesis relative to total liver protein synthesis. This decrease is accompanied by a proportional decline in the number of albumin-synthesizing polysomes, as determined by the binding of 125I-Labeled anti-albumin antibody, and indirect immunoprecipitation of [3H]leucine-labeled albumin-synthesizing polysomes. Furthermore, this decrease is associated with an equivalent reduction in the amount of total membrane-bound polysomes, whereas total free polysomes show little quantitative change. ⋯ The decrease in albumin production in the hypophysectomized rat, therefore, is apparently the result of a reduction in the amount of active albumin mRNA. The concomitant decrease in albumin-synthesizing polysomes appears to reflect a similar reduction in the amount of total membrane bound polysomes. Thus, a major physiological defect in hypophysectomy may be a preferential decline in membrane-bount polysomes accompanied by a reduction in mRNA levels, which is represented by the decrease in albumin synthesis.
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We present evidence that added thrombin stimulates release of endogenous arachidonic acid by suspensions of human platelets. We also show that added arachidonic acid causes a burst in O2 consumption that mimics one of the well described effects of thrombin on these cells. Further, added aspirin, a known inhibitor of the burst in O2 consumption caused by thrombin, also blunted the stimulatory effect of arachidonate on O2 consumption, and eicosatetraynoate, a known inhibitor of arachidonate oxygenation, blunted the burst in O2 consumption initiated by both thrombin and arachidonate. We conclude that rapid oxygenation of endogenously released arachidonic acid accounts for the thrombin-mediated burst in oxygen consumption by platelets.
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Effects of cyclic adenosine 3':5'-monophosphate (cyclic AMP)-dependent protein kinase were studied in sarcoplasmic reticulum prepared from cardiac and slow and fast (white) skeletal muscle. Cyclic AMP-dependent protein kinase failed to catalyze phosphorylation of fast skeletal muscle microsomes as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cyclic AMP-dependent protein kinase was without effect on calcium uptake by these microsomes. ⋯ A statistically significant increase in calcium uptake by these membranes was produced by the protein kinase. Increases in protein kinase-catalyzed phosphorylation of a low molecular weight microsomal component and in calcium transport by sarcoplasmic reticulum of cardiac and slow skeletal muscle may be related to the relaxation-promoting effects of epinephrine seen in these types of muscle. Conversely, the absence of a relaxation-promoting effect of epinephrine in fast skeletal muscle may be associated with the lack of effect of cyclic AMP and protein kinase on calcium transport by the sarcoplasmic reticulum of this type of muscle.
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Some effects of salts on the adenylate cyclase of partially purified plasma membranes from rat liver have been studied. Under conditions where cyclic adenosine 3':5'-monophosphate formation was linear with respect to time and protein concentration, the enzyme was stimulated 3- to 6-fold by 10 mM NaF, 10- to 30-fold by 1 muM glucagon, 4- to 5-fold by 0.1 mM 5'-guanylylimidodiphosphate, and in the presence of 3 muM GTP, 2-fold by 10 mug/ml of prostaglandin E1. Various salts were found to stimulate basal activity slightly, but enhanced the response to NaF 3- to 4-fold, to glucagon 1.5- to 2-fold, to 5'-guanylylimidodiphosphate 2- to 3-fold, and to prostaglandin E1 1.5-fold. ⋯ Enhancement of hormonal stimulation by NaN3 was also demonstrable with cardiac and adipose tissue adenylate cyclase. However, NaN3 did not stimulate detergent-dispersed adenylate cyclases from either liver plasma membranes or brain. The data suggest that stimulation of adenylate cyclase by salts may require the added presence of other stimulatory agents and an intact membrane structure.