Inhibition of glycine N-methyltransferase activity by folate derivatives: implications for regulation of methyl group metabolism

Glycine N-methyltransferase, an enzyme that uses S-adenosylmethionine to methylate glycine with the production of sarcosine, was recently shown to be identical with a major folate binding protein of rat liver (Cook, R.J. and Wagner, C. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 3631-3634). We now present evidence that 5-methyltetrahydropteroylpentaglutamate (5-CH3-H4PteGlu5) is bound with high specificity, and is a powerful inhibitor of the enzyme. It is proposed that this information may be used to modify the "methyl trap" hypothesis which describes how the availability of one-carbon units is regulated by folate, vitamin B12 and methionine.     

A comparison of in vivo catalysis by creatine kinase in avian skeletal muscles with different fibre composition

The maximum activity of creatine kinase in vitro is similar in the pectoralis major muscle of the chicken and the duck. However, the flux (phosphocreatine to ATP) as measured by 31P saturation transfer NMR in vivo is almost 2-fold higher in the duck. This apparent discrepancy can be accounted for by the differences in the cytosolic free ADP concentrations in resting muscle.     

The Pragmatics of Proverb Performances in New Mexican Spanish

Performances of proverbs by Mexicanos in northern New Mexico are characterized by seven features in addition to the proverb text. These are examined with respect for the role they play in connecting basic cultural and linguistic patterns with the minute details of an ongoing social interaction. The processes of presupposition and contextualization are identified as crucial determinants of the way each feature will be realized in a given performance.     

Effects of Neuronal Activity on Inositol Phospholipid Metabolism in the Rat Autonomic Nervous System

The effect of nerve stimulation on inositol phospholipid hydrolysis in autonomic tissue was assessed by direct measurement of [3H]inositol phosphate production in ganglia that had been preincubated with [3H]inositol. Within minutes, stimulation of the preganglionic nerve increased the [3H]inositol phosphate content of the superior cervical sympathetic ganglion indicating increased hydrolysis of inositol phospholipids. This effect was blocked in a low Ca2+, high Mg2+ medium. It was also greatly reduced when nicotinic and muscarinic antagonists were present together in normal medium. However, neither the nicotinic antagonist nor the muscarinic antagonist alone appeared to be as effective as both in combination. In other experiments, stimulation of the vagus nerve caused dramatic increases in [3H]inositol phosphate in the nodose ganglion but did not increase [3H]inositol phosphate in the nerve itself. This effect was insensitive to the cholinergic antagonists. Thus, neuronal activity increased inositol phospholipid hydrolysis in a sympathetic ganglion rich in synapses, as well as in a sensory ganglion that contains few synapses. In the sympathetic ganglion, synaptic stimulation activated inositol phospholipid hydrolysis and this was primarily due to cholinergic transmission; both nicotinic and muscarinic pathways appeared to be involved.     

The relationship between zeros and factors of binding polynomials and cooperativity in protein-ligand binding

Cooperativity in the protein-ligand binding process is discussed in terms of the zeros of the binding polynomial and the corresponding possible factorizations of the binding polynomial into polynomials having non-negative coefficients. Particular attention is paid to the case in which the real parts of all zeros are negative (Hurwitz polynomial) and the case in which the binding polynomial admits no positive factorization (positive irreducible polynomial). Such factorizations are then interpreted as site linkage patterns and related to cooperativity. The possible combinations of zeros of the binding polynomials for the MWC and KNF tetrahedral, square and linear models are determined and the corresponding factorization and linkage patterns analyzed. An application and interpretation are then made for data obtained from Trout I hemoglobin.     

Photochemical reactions in interstellar grains photolysis of co,NH3, and H2O

A simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH₃:H₂O gas mixture on an Al block at 10K, with concomitant irradiation with vacuum UV. The residues were analyzed by GC-MS, HPLC, and near IR; a reaction pathway leading from NH₃ to complex alcohol, fatty acid, and amide products in 27 stages is postulated. The astronomical relevance and significance of the observations are discussed.     

Concentrations of Homovanillic Acid and 5-Hydroxyindoleacetic Acid in Cerebrospinal Fluid from Human Infants in the Perinatal Period

To assess maturation of central serotonin and catecholamine pathways at birth, we measured lumbar CSF homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), stable acid metabolites of dopamine and serotonin, using HPLC with electrochemical detection. CSFs from 57 neonates (38 premature and 19 at term) and 13 infants 1-6 months old were studied. HVA levels increased with maturity (p less than 0.05; ANOVA), whereas 5-HIAA levels were similar in all these subjects. HVA/5-HIAA ratios increased markedly from 1 +/- 0.12 in the most premature neonates to 1.98 +/- 0.17 in the older infants (p less than 0.01; t test). There were no sex differences for these values.     

Lipolysis of serum-activated triacylglycerol at the surface of J774.1 macrophages

Summary Cultured mouse (J774.1) macrophages accumulated triacylglycerol, but no cholesteryl ester or cholesterol, when incubated in albumin-poor medium with serum-activated lipid particles containing 84 mol% trioleoylglycerol and 9 mol% cholesteryl oleate. Accumulation of triacylglycerol by cells was associated with hydrolysis of particulate triacylglycerol to fatty acid and glycerol. Both acyl and glyceryl moieties of particulate triacylglycerol were recovered in cellular triacylglycerol with a molar ratio of 3.6. The cells also accumulated fatty acid and monoacylglycerol. Whether acylglycerol was taken up as a single molecular species, such as monoacylglycerol, or as several species can not be determined by the present findings. Macrophages incubated with lipid particles for 24 h had many lipid particles attached to cell surfaces and numerous intracellular lipid droplets. The surface film of attached particles was continuous with the outer leaflet of plasma membrane of the cells. Particles partially depleted of core triacylglycerol and collapsed surface films were found attached to surfaces of macrophages. There was no morphological evidence that lipid particles were taken up intact by cells, through endocytosis or phagocytosis. Macrophages incubated with lipid particles also contained intracellular lamellar structures. They varied in size and shape, and were located in the periphery of cells, sometimes near lipid droplets and endoplasmic reticulum. Only 3% of the lamellar structures were associated with lysosomes, indicating they probably were not of lysosomal origin. Lipid particles attached to cells decreased in size and number, and lamellar structures developed at the surface of particles, or replaced the particles, when glutaraldehyde-fixed specimens were incubated at 25° C, demonstrating lipolytic activity at the surface of macrophages. Our findings suggest that particulate triacylglycerol was hydrolyzed by lipoprotein lipase at the surface of macrophages, and that fatty acid and monoacylglycerol formed by lipolysis were transported directly into the cells to be reesterified. When lipolytic products were taken up faster than they could be utilized, they accumulated as lamellar structures in the cells.Abbreviations MEM Eagle's alpha modification of minimum essential medium     

Enterotoxin A production in Staphylococcus aureus: inhibition by glucose

In this study, we investigated the relationship between carbohydrate metabolism and repression of staphylococcus enterotoxin A (SEA) in Staphylococcus aureus 196E and a pleiotrophic mutant derived from strain 196E. The mutant, designated at strain 196E-MA, lacked a functional phosphoenolpyruvate phosphotransferase system (PTS). The mutant produced acid, under aerobic conditions, from only glucose and glycerol. The parent strain contained an active PTS, and aerobically produced acid from a large number of carbohydrates. Prior growth in glucose led to repression of SEA synthesis in the parent strain; addition to the casamino acids enterotoxin production medium (CAS) led to more severe repression of toxin synthesis. The repression was not related to pH decreases produced by glucose metabolism. When S. aureus 196E was grown in the absence of glucose, there was inhibition of toxin production as glucose level was increased in CAS. The inhibition was related to pH decrease and was unlike the repression observed with glucose-grown strain 196E. The inhibition of SEA synthesis in mutant strain 196E-MA was approximately the same in cells grown with or without glucose and was pH related. Repression of SEA synthesis similar to that seen with glucose-grown S. aureus 196E could not be demonstrated in the mutant. In addition, glucose-grown S. aureus 196E neither synthesized -galactosidase nor showed respiratory activity with certain tricarboxylic acid (TCA) cycle compounds. Glucose-grown strain 196E-MA, however, did not show supressed respiration of TCA cycle compounds; -galactosidase was not synthesized because the mutant lacked a functional PTS. Cyclic adenosine-3, 5-monophosphate did not reverse the repression by glucose of SEA or -galactosidase synthesis in glucose-grown S. aureus 196E. An active PTS appears to be necessary to demonstrate glucose (catabolite) repression in S. aureus.Abbreviations SEA staphylococcal enterotoxin A - SEB staphylococcal enterotoxin B - SEC staphylococcal enterotoxin C - PTS phosphoenolpyruvate phosphotransferase system - CAS casamino acids salts medium - TCA tricarboxylic acid cycle     

Superoxide production by polymorphonuclear leukocytes

Summary Phagocytosis by polymorphonuclear leukocytes triggers a burst of oxidative metabolism resulting in hydrogen peroxide and superoxide production, and these active oxygen species function in the killing of microorganisms. A new cytochemical technique, based on a manganese dependent diaminobenzidine oxidation, has been developed to detect superoxide in these cells. It has been shown that superoxide generation is associated with the plasma membrane in cells activated by particulate (zymosan) and nonparticulate (phorbol myristate acetate) stimuli. This membraned activity is maintained during invagination such that reduced oxygen is generated within the endocytic vacuoles. Reaction product is absent from unstimulated cells; additionally, formation of precipitate is blocked by omission of Mn⁺⁺, low temperature, glutaraldehyde prefixation, and the presence of superoxide dismutase in the incubation medium.In honour of Prof. P. van Duijn