Rapid relaxation of single frog skeletal muscle fibres following laser flash photolysis of the caged calcium chelator, diazo-2

Diazo-2 is a calcium chelator based on BAPTA [(1989) J. Biol. Chem., in press], whose electron withdrawing diazoacetyl group may be rapidly (2000 s-1) converted photochemically to an electron donating carboxymethyl group by exposure to near ultraviolet light, producing an increase in its calcium affinity (Kd changes from 2.2 microM to 0.073 microM) without steric modification of the metal binding site. Photolysis of a 2 mM solution of this compound with a brief flash of light from a frequency-doubled ruby laser (347 nm) caused single skinned muscle fibres from the semitendinosus muscle of the frog Rana temporaria to relax with a mean half-time of 60.4 +/- 5 ms (range 30-100 ms, n = 15) at 12 degrees C, which is faster than the relaxation observed in intact muscles (half-time 133 ms at 14 degrees C [(1986) J. Mol. Biol. 188, 325-342]) and similar to the rate of the fast phase of tension decay in intact single fibres (20 s-1 at 10 degrees C [(1982) J. Physiol. 329, 1-20]).     

How soon after myocardial infarction should plasma lipid values be assessed?

Because acute myocardial infarction may affect plasma lipid concentrations it is commonly recommended that assessment of these concentrations should be delayed until about three months after the acute event. A study was therefore conducted of fasting plasma lipid concentrations in 58 patients with acute myocardial infarction. Measurements were made during their stay in hospital (days 1, 2, and 9) and three months later. Triglyceride concentrations remained unchanged throughout. Values of total cholesterol, low density lipoprotein, and high density lipoprotein all fell significantly between the first two days and day 9. Total cholesterol and low density lipoprotein also showed significant falls between days 1 and 2. Nevertheless, fasting plasma lipid concentrations showed no significant difference at any time during the first 48 hours from values measured three months later. After the infarction 26 patients changed to eating less fat or less energy, or both. More patients had hypercholesterolaemia in the first 48 hours than at three months. These results suggest that lipid state may be assessed as accurately, and possibly more accurately, during the first 48 hours after acute myocardial infarction than at three months.     

Liver,but Not Muscle,Has an Entrainable Metabolic Memory

Hyperglycemia in the hospitalized setting is common, especially in patients that receive nutritional support either continuously or intermittently. As the liver and muscle are the major sites of glucose disposal, we hypothesized their metabolic adaptations are sensitive to the pattern of nutrient delivery. Chronically catheterized, well-controlled depancreatized dogs were placed on one of three isocaloric diets: regular chow diet once daily (Chow) or a simple nutrient diet (ND) that was given either once daily (ND-4) or infused continuously (ND-C). Intraportal insulin was infused to maintain euglycemia. After 5 days net hepatic (NHGU) and muscle (MGU) glucose uptake and oxidation were assessed at euglycemia (120 mg/dl) and hyperglycemia (200 mg/dl) in the presence of basal insulin. While hyperglycemia increased both NHGU and MGU in Chow, NHGU was amplified in both groups receiving ND. The increase was associated with enhanced activation of glycogen synthase, glucose oxidation and suppression of pyruvate dehydrogenase kinase-4 (PDK-4). Accelerated glucose-dependent muscle glucose uptake was only evident with ND-C. This was associated with a decrease in PDK-4 expression and an increase in AMP-activated protein kinase (AMPK) phosphorylation. Interestingly, ND-C markedly increased hepatic FGF-21 expression. Thus, augmentation of carbohydrate disposal in the liver, as opposed to the muscle, is not dependent on the pattern of nutrient delivery.     

Substrate specificity determinants for casein kinase II as deduced from studies with synthetic peptides

The specificity of casein kinase II has been further defined by analyzing the kinetics of phosphorylation reactions using a number of different synthetic peptides as substrates. The best peptide substrates are those in which multiple acidic amino acids are present on both sides of the phosphorylatable serine or threonine. Acidic residues on the NH2-terminal side of the serine (threonine) greatly enhance the kinetic constants but are not absolutely required. Acidic residues on the COOH-terminal side of the serine (threonine) are absolutely required. One position for which the occupation of an acidic residue is especially critical is the position located 3 residues to the COOH terminus of the phosphate acceptor site, although the presence of an acidic amino acid in the positions that are 4 or 5 residues removed may also provide an appropriate structure that will serve as a substrate for the kinase. Aspartate serves as a better amino acid determinant than glutamate. A relatively short sequence of amino acids surrounding the phosphate acceptor site appears to serve as the basis for the specificity of casein kinase II. The peptides in this study were also assayed with casein kinase I and the casein kinase from the mammary gland so that the specificities of these kinases could be compared to that of casein kinase II.     

Correlation of nitrogen metabolism with biosurfactant production by Pseudomonas aeruginosa

A direct relationship between increased glutamine synthetase activity and enhanced biosurfactant production was found in Pseudomonas aeruginosa grown in nitrate and Proteose Peptone media. A chloramphenicol-tolerant strain showed a twofold increase in biosurfactant production and glutamine synthetase activity. Increased ammonium and glutamine concentrations repressed both phenomena.