The modulation of membrane fluidity by hydrogenation processes. III. The hydrogenation of biomembranes of spinach chloroplasts and a study of the effect of this on photosynthetic electron transport

A method is reported for the in situ modification of the lipids of isolated spinach chloroplast membranes. The technique is based on a direct hydrogenation of the lipid double bonds in the presence of the catalyst, chlorotris(triphenylphosphine)rhodium (I). The pattern of hydrogenation achieved suggests that the catalyst distributes amongst all of the membranes. The polyunsaturated lipids within the membranes are hydrogenated at a faster rate and at an earlier stage than are the monoenoic lipids.Whilst addition of the catalyst to the chloroplast causes an initial 10–20% decrease in Hill activity, saturation of up to 40% of the double bonds present can be accomplished without causing further significant alterations in photosynthetic electron transport processes or marked morphological changes of the chloroplast structure as observed in the electron microscope.     

Isozymes of the glycolytic and pentose-phosphate pathways in storage tissues of different oilseeds

Isozymes of hexose-phosphate isomerase (HPI; EC 5.3.1.9), pyruvate kinase (PK; EC 2.7.1.40) and 6-phosphogluconate dehydrogenase (6PGDH; EC 1.1.1.44) have been detected in the developing cotyledons of soybean (Glycine max (L.) Merr.), safflower (Carthamnus tinctorius L.) and sunflower (Helianthus annuus L.). In each seed there are two isozymes each of PK and HPI. The isozyme patterns of 6PGDH are more complex: soybean has two forms of the enzyme, safflower three, and sunflower six. In each tissue, at least 25% of the activity of each of the three enzymes is in the plastids. This supports the proposal that the glycolytic and pentose-phosphate pathways are operating in the plastids and that the plastids are the site of long-chain fatty-acid biosynthesis in developing oilseeds.Abbreviations HPI hexose-phosphate isomerase - 6PGDH 6-phosphogluconate dehydrogenase - PK pyruvate kinase     

Protease-nexin: A cellular component that links thrombin and plasminogen activator and mediates their binding to cells

This report identifies a component of normal human fibroblasts that forms a covalent linkage with thrombin and urokinase (urinary plasminogen activator) and mediates most of the specific cellular binding of these proteases. This component, here named protease-nexin (PN), is both associated with the cell surface and released into the culture medium. In several ways PN resembles antithrombin III (AT3), a prominent inhibitor of thrombin in serum: PN links thrombin, probably via an ester bond; PN does not link thrombin blocked at its catalytic site serine; PN has a high-affinity heparin-binding site; and heparin greatly accelerates the rate of linkage between soluble PN and thrombin. Despite these similarities, PN and AT3 are distinct; they differ in size and are not immunologically cross-reactive. Whereas AT3 regulates the proteolytic activity of thrombin in serum, PN may regulate the activity of serine proteases at and near the cell surface.     

Expression of a subgenomic retroviral messenger RNA

When mRNA for avian retroviral envelope glycoprotein (env) was injected into cells transformed by env-deficient Bryan Rous sarcoma virus, the env deficiency of the injected cells was complemented to allow the release of transforming virus for up to 40 hr. When virus spread within the injected culture was allowed to occur, a second phase of transforming virus production by the injected culture began approximately 2 days following injection, continued for many days and often increased to titers well above those seen soon after injection. The requirement for virus spread, along with the genetic properties of virus released long after injection, supported the hypothesis that the second phase of virus production resulted when injected env mRNA was packaged into virus released by injected cells. When this virus infected other cells within the culture the env mRNA was reverse-transcribed to form a subgenomic, proviral-like molecule able to direct the synthesis of env mRNA. Accordingly, it was shown that neither DNA nor full genomic viral RNA contaminating injected mRNA preparations could account for the results. Evidence that an mRNA can be reverse-transcribed into an active, proviral-like molecule may be of importance in the relationship between retroviruses and their hosts.     

Biosynthesis of mammalian glycoproteins. Glycosylation pathways in the synthesis of the nonreducing terminal sequences.

Six purified glycosyltransferase (a beta-galactoside alpha 2 leads to 6 sialyltransferase, a beta-galactoside alpha 2 leads to 3 sialyltransferase, an alpha-N-acetylgalactosaminide alpha 2 leads to 6 sialyltransferase, a beta-galactoside alpha 1 leads to 2 fucosyltransferase, a beta-N-acetylglucosaminide alpha 1 leads to 3 fucosyltransferase, and a (fucosyl alpha 1 leads to 2) galactoside alpha 1 leads to 3 N-acetyl-galactosaminyltransferase) have been used to study the biosynthetic pathways for formation of the nonreducing terminal oligosaccharide sequences in mammalian glycoproteins. The two glycoproteins used as model acceptor substrates in this study were human asialotransferrin, which contains the nonreducing terminal oligosaccharide sequence Gal beta 1 leads to 4GlcNAc beta 1 leads to 2Man, and antifreeze glycoprotein, which contains oligosaccarides with the structure, Gal beta 1 leads to 3GalNAc alph 1 leads O-Thr. Sequential action of the six glycosyltransferases on these model substrates led to the formation of previously described oligosaccharide structures. The studies reported here indicate that the substrate specificities of the individual enzymes dictate the structures that can be synthesized and the pathways by which they may be formed. The actions of a number of the transferasesare mutually exclusive, thereby prohibiting the formation of theoretically possible oligosaccharide structures. Oligosaccharides with the terminal sequence NeuAc alpha 2 leads to 3(Fuc alpha 1 leads to 2)Gal beta 1 leads to 3GalNAc and NeuAc alpha 2 leads to 6Gal beta 1 leads to 4(Fuc alpha 1 leads to 3)GlcNAc cannot be formed because the prior incorporation of sialic acid by the sialyltransferases yields products that are not acceptor substrates for the fucosyltransferases, and vice versa. Synthesis of other products requires that the enzymes act sequentially in a specific order. The structures NeuAc alpha 2 leads to 6(Fuc alpha 1 leads to 2)Gal beta 1 leads to 4GlcNAc, Fuc alpha 1 leads to 2Gal beta 1 leads to 4(Fuc alpha 1 leads to 3)GlcNAc, GalNAc alpha 1 leads to 3(Fuc alpha 1 leads to 2)Gal beta 1 leads to 4GlcNAc, and GalNAc alpha 1 leads to 3(Fuc alpha 1 leads to 2)Gal beta 1 leads to 3GalNAc can only be synthesized if the fucosyl alpha 1 leads to 2 galactose linkage is formed first. Synthesis of the pentasaccharide sequences GalNAc alpha 1 leads to 3(Fuc alpha 1 leads to 2)Gal beta 1 leads to 3(NeuAc alpha 2 leads to 6)GalNAc and GalNAc alpha 1 leads to 3(Fuc alpha 1 leads to 2)Gal beta 1 leads to 4(Fuc alpha 1 leads to 3)GlcNAc requires that the N-acetylgalactosaminyltransferase act last on the former structure and that the alpha 1 leads to 3 fucosyltransferase act last on the latter. In those instances where a product can be formed by one of two possible pathways, the comparisons of reaction rates indicate that one pathway is usually preferred...     

Foliar nectar production and ant activity on a neotropical tree,Ochroma pyramidale

Summary In second growth forest in lowland Costa Rica, ants forage at the foliar nectaries of juvenile Ochroma pyramidale. The relationship between leaf development, foliar nectar production and ant visitation indicates that nectar secretion and ant maintenance are greatest following rapid leaf expansion. Nectar measurements in the glasshouse corroborate field measurements showing that nectar production on a sapling is continuous through time and correlated with distribution and abundance of ants within a sapling. The presence of two nectary types, leaf vein and petiolar, on the leaves of O. pyramidale results in the continual maintenance of ants on the leaf undersurface. Nectar production of a sapling increases with increasing leaf area resulting in greater number of ants per sapling. Energetic costs of nectar production and ant maintenance appear low, representing about one per cent of the total energy invested in leaves.Spatial and diurnal patterns of ant activity changed very little over the study period. Removal and exclusion of ants from saplings results in the utilization of foliar nectar by trigonid bees. A significant difference in leaf damage between ant-visited and unvisited saplings, coupled with ant behavioral characteristics, is consistent with the hypothesis that ants act as antiherbivore agents on Ochroma.     

Prostaglandin E1 effects on resting and cholinergically stimulated lower esophageal sphincter pressure in cats

Intraluminal esophageal manometry with a sleeve catheter was used to compare the magnitude of decrease in lower esophageal spincter (LES) pressure produced by an arterial or venous infusion of prostaglandin E₁ in cats. Arterial PGE₁ produced significantly lower LES pressures than venous PGE₁ (p < 0.05). Maximal decrease of 75% in basal LES pressure occurred with an associated 15% decrease in systolic blood pressure. The site of action of PGE₁ in producing LES hypotension was studied by injection of either edrophonium, or bethanechol during the maximal PGE₁ effects. Bethanechol, which acts directly on sphincteric smooth muscle, produced an increase in LES pressure during both saline and PGE₁ infusion, while the increases in LES pressure seen with edrophonium during saline infusion were blocked during the PGE₁ infusion. From these studies, we conclude that PGE₁ produces LES hypotension in the cat by an inhibitory effect on the cholinergic pathway responsible for maintaining LES tone. These studies pharmacologically reproduce the LES pressure abnormality previously reported in the cat during acid-induced esophagitis and support the hypothesis that PGE₁ may be involved in the pathogenesis of acute acid-induced lower esophageal sphincter abnormalities.     

POLLEN MORPHOLOGY OF HAPLOPAPPUS AND RELATED GENERA (COMPOSITAE—ASTEREAE)

Pollen grains of Haplopappus and related genera in the subtribe Solidaginae from North and South America were examined by light and scanning electron microscopy. The grains are consistently tricolporate and echinate. Some genera can be distinguished by pollen size, spine length, and number of spine rows between colpi. Based on these characters, the divergence of Benitoa from other members of the subtribe, as indicated by its morphology and secondary chemistry, is supported. Additionally, the recently suggested absence of a close relationship between Pyrrocoma and Oonopsis is indicated by their contrasting pollen types. This study demonstrates the potential of pollen studies in distinguishing some taxonomic groups in the Astereae.     

Metabolism and transport of glutamine and glucose in vascularly perfused small intestine of the rat

1. The proportion of active (dephosphorylated) pyruvate dehydrogenase in rat heart mitochondria was correlated with total concentration ratios of ATP/ADP, NADH/NAD+ and acetyl-CoA/CoA. These metabolites were measured with ATP-dependent and NADH-dependent luciferases. 2. Increase in the concentration ratio of NADH/NAD+ at constant [ATP]/[ADP] and [acetyl-CoA]/[CoA] was associated with increased phosphorylation and inactivation of pyruvate dehydrogenase. This was based on comparison between mitochondria incubated with 0.4mM- or 1mM-succinate and mitochondria incubated with 0.4mM-succinate+/-rotenone. 3. Increase in the concentration ratio acetyl-CoA/CoA at constant [ATP]/[ADP] and [NADH][NAD+] was associated with increased phosphorylation and inactivation of pyruvate dehydrogenase. This was based on comparison between incubations in 50 micrometer-palmitotoyl-L-carnitine and in 250 micrometer-2-oxoglutarate +50 micrometer-L-malate. 4. These findings are consistent with activation of the pyruvate dehydrogenase kinase reaction by high ratios of [NADH]/[NAD+] and of [acetyl-CoA]/[CoA]. 5. Comparison between mitochondria from hearts of diabetic and non-diabetic rats shows that phosphorylation and inactivation of pyruvate dehydrogenase is enhanced in alloxan-diabetes by some factor other than concentration ratios of ATP/ADP, NADH/NAD+ or acetyl-CoA/CoA.