Creatine phosphokinase activity in dysgenic (mdg/mdg) mouse muscle

The specific activity of creatine phosphokinase (CPK) was measured in the muscle of mdg/mdg and control embryos of 14-18 days' gestation. CPK specific activity values were similar in mutant and normal embryos at the earliest stages examined (14-15 days). However, after 15 1/2 days, the specific activity of the enzyme in the mdg/mdg embryos was approximately 50% lower than in the controls. The dysgenic and normal muscle extracts exhibited comparable stability after storage at -85 C. CPK activity levels in the muscle of adult heterozygotes (+/mdg) and wild-type (+/+) controls were found to be statistically identical. The findings suggest that the mdg mutation does not have a primary or direct effect on CPK activity.     

Iron mobilization from ferritin by chelating agents

The release of iron from horse spleen ferritin by the chelating agents desferrioxamine B, rhodotorulic acid, 2,3-dihydroxybenzoate, 2,2′-bipyridyl and pyridine-2-aldehyde-2-pyridyl hydrazone (Paphy) has been studied in vitro. Ferritin prepared by classical procedures involving thermal denaturation releases its iron less effectively than ferritin isolated by a modified procedure that avoids this step. Desferrioxamine B and rhodotorulic acid are the most effective in releasing iron from both preparations of ferritin. When FMN is added, iron release by desferrioxamine B, rhodotorulic acid, and 2,3-dihydroxybenzoate was effectively blocked, whereas both bipyridyl and Paphy showed a marked simulation. A substantial increase in iron release was also observed for bipyridyl and Paphy with ascorbate; a less important increase was noted for rhodotorulic acid. EDTA exerted a marked inhibition of iron release from ferritin with rhodotorulic acid, 2,3-dihydroxybenzoate, bipyridyl, and Paphy. The effects of citrate and oxalate on iron release by the chelators was small. The effect of the concentration of flavin on iron release from ferritin by bipyridyl and desferrioxamine B have been studied. Desferrioxamine is unable to mobilize FeII from ferritin following reduction by reduced FMN, whereas bipyridyl can rapidly complex the ferrous iron. The results are discussed in the context of our current concepts of storage iron mobilization in the treatment of iron overload.     

Specific inactivation of lysosomal glycosidases in living fibroblasts by the corresponding glycosylmethyl-p-nitrophenyltriazenes.

Glicentin (a highly purified 100-amino acid peptide with glucagon-like immunoreactivity from porcine gut) was subjected to limited digestion with trypsin and carboxypeptidase B, and the resulting peptides were studied by gel filtration and region-specific glucagon radioimmunoassays. Similar digests of glucagon and purified fragments of glucagon were studied in parallel. Glicentin gave rise to peptides that corresponded closely to the 1-17 and 19-29 fragments of glucagon. Also, 125I-labelled glicentin and 125I-labelled glucagon gave rise to identical fragments after trypsin treatment. On the basis of this and other evidence [Jacobsen, Demandt, Moody & Sundby (1977) Biochim. Biophys. Acta 493, 452-459] it is concluded that glicentin contains the entire glucagon sequence at residues number 64-92 and thus fulfills one of the requirements for being a 'proglucagon'.     

Effects of Controlled Atmospheres on Production of Sesquiterpenoid Stress Metabolites by White Potato Tuber: Possible Involvement of Cyanide-resistant Respiration

Levels of katahdinone (solavetivone), lubimin, rishitin, and phytuberin, sesquiterpenoid stress metabolites of white potato (Solanum tuberosum), were monitored in tuber slices which were challenged with an extract of Phytophthora infestans and incubated under controlled atmospheres. A mixture of ethylene in air enhanced stress metabolite production. This enhancement was amplified by higher partial pressures of oxygen. Stress metabolite production was inhibited by salicylhydroxamic acid. These results suggest the involvement of cyanide-resistant respiration in the production of potato stress metabolites, compounds which may serve as phytoalexins.     

Serratia species isolated from plants

Using the selective caprylate-thallous agar medium, the presence ofSerratia species was systematically examined in 623 plant samples. A total of 167Serratia strains was isolated from these plant samples and identified to species and biogroups. Uniform and characteristicSerratia populations were found in figs and coconuts: (i)Serratia ficaria was recovered from most figs collected in California, Tunisia, and France; various biotypes ofS. marcescens also were found in figs; (ii) onlyS. marinorubra was recovered from coconuts bought on two continents. From plants other than figs and coconuts, representatives were isolated of all eightSerratia species we presently recognize—with a large preponderance ofS. liquefaciens andS. proteamaculans. These other plant samples fell into threeSerratia-prevalence groups: (i) vegetables-mushrooms-mosses-decaying plant material (53.8% of these samples were positive forSerratia); (ii) grasses (23.7% positive); and (iii) trees and shrubs-small plants (8.4% positive). PigmentedS. marcescens biotypes were rarely isolated from plants (except from figs). Of theS. marcescens biogroups most frequently encountered in nosocomial and iatrogenic infections of man, A3 and A4 were isolated from plants in this study, but A5/8 and TCT were not.     

Insulin release: Reconciliation of the receptor and metabolic hypotheses

Summary Nutrients which stimulate insulin secretion are currently thought to initiate the series of cellular events eventually leading to insulin release either by interacting with a stereospecific receptor system (the regulatory site hypothesis) or by acting as a fuel (the substrate site hypothesis) in the pancreaticB-cell. The latter hypothesis is supported by a number of observations indicating that the capacity of nutrients to stimulate insulin release is indeed highly dependent on their capacity to increase catabolic fluxes in isolated pancreatic islets. However, these observations do not rule out the existence of nutrient receptors in islet cells. For instance, a nonmetabolized analog of L-leucine stimulates insulin release by causing allosteric activation of glutamate dehydrogenase, which should be considered, therefore, as a receptor for certain amino acids. Likewise, the increase in glycolytic flux, which is associated with the process of glucose-stimulated insulin release, is attributable not solely to a mass action phenomenon but also to the activation of phosphofructokinase by fructose 2.6-bisphosphate. The biosynthesis of this activator may involve a glucose receptor system. The fact that certain nutrient secretagogues (e.g D-glucose and L-leucine) act in the B-cell both as substrates and enzyme activators permits reconciliation of the substrate site and regulatory site hypotheses for insulin release.     

Absolute configurations of isoflavans

The absolute configurations of isoflavans and isoflavanquinones isolated from Cyclolobium, Dalbergia and Machaerium species were established by comparison of their ORD curves with that of (3S)-5,7,3′,4′-tetra-methoxyisoflavan and (3S)-7,4′-dimethoxyisoflavan-2′,5′-quinone, respectively. The assignments were checked by the ozonolysis of the isoflavan (?)-duartin to (R)-paraconic acid and the oxidation of isoflavans to isoflavanquinones. The PMR spectra of the dihydropyran ring of the isoflavans are discussed in terms of the preferred conformation of this ring.     

Characterization and determination of titratable groups of proteins by linearization of titration curves. II. Application to lysozyme

The potentiometric acid-base titration curve of fully protonated lysozyme at ionic strengths of 0.10 and 1.0 m has been performed. The stoichiometry and the pK_a values of each titratable group have been determined through the linearization of titration curves. Two types of carboxylic groups with pK_a values of 3.76 and 5.02, the imidazole group with pK_a 7.37 and the amine group with pK_a 9.63, have been identified at an ionic strength of 0.10 m at 25.0°C. The number of titratable groups found per mole of protein has been 5.12 and 5.60 for the two types of carboxylic groups, 1.13 for the imidazole group, and 3.19 for the amino groups. The endpoint of the titration of the protein obtained by this method accords quite well with the endpoint obtained by the use of Gran function applied to the excess of strong base.