Some growth and metabolic characteristics of monensin-sensitive and monensin-resistant strains of Prevotella (Bacteroides) ruminicola.

New strains with enhanced resistance to monensin were developed from Prevotella (Bacteroides) ruminicola subsp. ruminicola 23 and P. ruminicola subsp. brevis GA33 by stepwise exposure to increasing concentrations of monensin. The resulting resistant strains (23MR2 and GA33MR) could initiate growth in concentrations of monensin which were 4 to 40 times greater than those which inhibited the parental strains. Resistant strains also showed enhanced resistance to nigericin and combinations of monensin and nigericin but retained sensitivity to lasalocid. Glucose utilization in cultures of the monensin-sensitive strains (23 and GA33) and one monensin-resistant strain (23MR2) was retarded but not completely inhibited when logarithmic cultures were challenged with monensin (10 mg/liter). Monensin challenge of cultures of the two monensin-sensitive strains (23 and GA33) was characterized by 78 and 51% decreases in protein yield (milligrams of protein per mole of glucose utilized), respectively. Protein yields in cultures of resistant strain 23MR2 were decreased by only 21% following monensin challenge. Cell yields and rates of glucose utilization by resistant strains GA33MR were not decreased by challenge with 10 mg of monensin per liter. Resistant strains produced greater relative proportions of propionate and less acetate than the corresponding sensitive strains. The relative amounts of succinate produced were greater in cultures of strains 23, GA33, and 23MR2 following monensin challenge. However, only minor changes in end product formation were associate with monensin challenge of resistant strain GA33MR. These results suggest that monensin has significant effects on both the growth characteristics and metabolic activities of these predominant, gram-negative ruminal bacteria.     

AGE STRUCTURE OF PHORADENDRON JUNIPERINUM (VISCACEAE), A XYLEM-TAPPING MISTLETOE: INFERENCES FROM A NON-DESTRUCTIVE MORPHOLOGICAL INDEX OF AGE

We investigated the age-structure of the xylem-tapping mistletoe Phoradendron juniperinum in relation to characteristics of its host tree, Juniperus osteosperma. We first correlated branch structure in the mistletoe with age of the mistletoe infection as determined anatomically; this correlation provided a nondestructive, field method of obtaining age structure information. We then surveyed the mistletoe plants, applying our aging index, within a population of their host trees in southwestern Utah; the majority of mistletoe plants were 2–12 years old. This peak in abundance of mistletoe infections showed no correlation to total annual precipitation within or 1 year previous to the peaks, minimum winter temperature, or to warmer than average winter temperatures. However, there was a positive correlation (r = 0.51, P < 0.06) with the amount of summer precipitation. A log-linear analysis indicated that a greater than expected number of mistletoe infections occurred at 5–7 years of age and at approximately 3 m in height among all host trees. We suggest that this pattern resulted because this canopy position had greater leaf and branch areas and was visited most frequently by seed-dispersing birds. The log-linear analysis also revealed that fewer than expected mistletoe infections occurred at ages older than 10 years, yet our data indicate that plants can reach 20 years of age. The lack of infections > 10 years of age was correlated to a period of below average precipitation, especially during the growing season, but not with cold winter temperatures, which in other studies had been suggested as a factor influencing mortality. We feel that drought may play an important role in influencing mistletoe mortality through its direct affect on host tree water status, but in addition we offer two alternative hypotheses to explain mistletoe longevity; the first is concerned with the relationship between carbon and nitrogen costs and maintaining large leaf areas in older plants, and the second addresses how increased hydraulic resistance in older and larger plants may be too costly for the plant, and stems are abscised.     

The stimulation of the brain alkaline phospholipase A1 attacking phosphatidylethanolamine by various salts and metal chelators

Rat brain contains a soluble, high molecular weight phospholipase A₁ of alkaline pH optimum which shows a preference for phosphatidylethanolamine as substrate. There is evidence that the same enzyme exists in liver and kidney. At low osmotic concentrations of buffer the enzyme is markedly stimulated by CaCl₂. However, MgCl₂ and MnCi₂ are equally as effective although at concentrations above 2 mM the activation falls away with MnCl₂. The phospholipase A₁ is stimulated by divalent metal ion chelators (EDTA, EGTA, CDTA) and by sodium phosphate and sodium sulphate. The activity is inhibited by hexanol, benzyl alcohol, diethylether and detergents. Although the activity can be inhibited by saturated and unsaturated fatty acids, no evidence could be obtained that the activators function by counteracting the inhibitory action of fatty acids liberated at the interface of the substrate and incubation medium. It is suggested that to achieve good enzymic hydrolysis a certain type of organised hydrated phosphatidylethanolamine structure is required in which the negative zeta potential has been reduced by metallic cations in the incubation medium.This paper is dedicated to Dr. Derek Richter on his seventy-fifth birthday.     

Uptake of [3H]threonine in human colonic mucosa associated with carcinoma: An autoradiographic analysis at the ultrastructural level

Summary The uptake ofd,l-[G-³H]threonie was studied to show cellular protein synthesis, at the ultrastructural level, as part of our investigation into alterations in glycoprotein synthesis which occur in colonic mucosa adjacent to carcinoma (transitional mucosa). Threonine uptake, though variable, was higher in transitional than in normal mucosa. Most of the threonine was incorporated into the endoplasmic reticulum of the immature cells at the bottom of the crypt. With longer isotope incubation, activity was found in other organelles in cells which were still undifferentiated or immature or both.From our data, the increased uptake of [³H]threonine in transitional mucosa, seems to be the result of prolonged protein synthesis associated with an extension of the cellular proliferation zone in the crypt, rather than being the effect of increased cell turnover. Thus, variations in [³H]threonine uptake are not related to the changes in the rate of galactose incorporation in mucosa adjacent to carcinoma.     

Possible Role of Cyclic AMP in the Receptor-Mediated Regulation of Glycosyltransferase Activities in Neurotumor Cell Lines

Exposure of mouse neuroblastoma cell line N4TGl to opiates or [D-Ala2,D-Leu5] enkephalin produced a naloxone-reversible inhibition of cyclic AMP synthesis and prevented, in a concentration-dependent manner, the formation of both ganglioside GM2 (GalNAc-[NeuNAc]-Gal-Glc-ceramide) from GM3 (NeuNAc-Gal-Glc-ceramide) and ganglioside GM1 (Gal-GalNAc-[NeuNAc]-Gal-Glc-ceramide) from GM2 in cell-free extracts. In contrast, the receptor-mediated elevation of intracellular cyclic AMP levels by agents such as prostaglandin E1 (in the presence of isobutylmethylxanthine) or the addition of the cyclic AMP derivatives (dibutyryl cyclic AMP) markedly stimulated the activities of UDP-GalNAc:GM3,N-acetylgalactosaminyltransferase and UDP-Gal:GM2,galactosyltransferase. An overall increase in the synthesis of gangliosides more complex than GM3 was also observed in the mouse neuroblastoma x hamster brain explant hybrid cell line NCB-20 following elevation of cyclic AMP levels by treatment with serotonin and pargyline. The data presented support the hypothesis that cyclic AMP may have a role in the regulation of sialoglycosphingolipid biosynthesis.     

Quantitative analysis of metabolite levels in normal human subjects by31P topical magnetic resonance

Conclusions The results we have obtained on forearm muscles of normal human subjects are complementary to those on isolated frog muscle and they lead, to the same conclusions. We are satisfied that our³¹P TMR measurements of [P-metabolites] in normal subjects are reliable, and we are now extending these methods for use in cases of degenerative muscular disorders (Edwards et al., 1982). Chemical estimates of [ADP] and [AMP] are not directly relevant to metabolic studies, and so an important contribution of NMR to the study of muscular mechanisms is its ability to estimate the concentrations of these metabolites that are free to take part in metabolic reactions.     

The kinetics of rat liver and heart mitochondrial beta-hydroxybutyrate dehydrogenase.

The kinetic mechanisms of the beta-hydroxybutyrate dehydrogenase from rat heart and liver mitochondria were investigated. Both enzymes, show an Ordered Bi Bi mechanism and there are no major differences in the kinetic constants. In both cases, the solubilized enzyme, re-activated with phosphatidylcholine, shows kinetic properties very similar to those of the enzyme bound to the mitochondrial membrane.     

Biopterin

An enzyme that catalyzes the conversion of 2-amino-6-(5'-triphosphoribosyl)amino-5- or 6-formamido-6-hydroxypyrimidine, but not of guanosine triphosphate, to quinonoid 6-(D-erythro-1'-2'-3'-trihydroxypropyl)dihydropterin triphosphate and formic acid has been purified to homogeneity from some mammalian brain and liver. The enzyme of a single strand is a basic protein of 9177 daltons consisting of 68 amino acid residues--except the enzyme from rat brain, which has one additional aspartic acid as residue 7. The enzyme possesses three free SH groups and, in its most active form, 1 mol of phosphate per mole of enzyme. Peptides isolated after hydrolysis with trypsin, chymotrypsin, or weak acid were separated by thin-layer chromatography and sequenced manually by Edman degradation. The complete sequence of the molecule was established as follows: (formula: see text)