Light modulation of the activity of carbon metabolism enzymes in the crassulacean Acid metabolism plant kalanchoë

When intact Kalanchoë plants are illuminated NADP-linked malic dehydrogenase and three enzymes of the reductive pentose phosphate pathway, ribulose-5-phosphate kinase, NADP-linked glyceraldehyde-3-phosphate dehydrogenase, and sedoheptulose-1,7-diphosphate phosphatase, are activated. In crude extracts these enzymes are activated by dithiothreitol treatment. Light or dithiothreitol treatment does not inactivate the oxidative pentose phosphate pathway enzyme glucose-6-phosphate dehydrogenase. Likewise, neither light, in vivo, nor dithiothreitol, in vitro, affects fructose-1,6-diphosphate phosphatase. Apparently the potential for modulation of enzyme activity by the reductively activated light effect mediator system exists in Crassulacean acid metabolism plants, but some enzymes which are light-dark-modulated in the pea plant are not in Kalanchoë.     

Isopropyl-β-d-thiogalactopyranoside influences the metabolism of Escherichia coli

Summary Addition of isopropyl -D-thiogalactopyranoside (IPTG) to a strain of Escherichia coli with one lac promoter in its chromosome causes reduction in synthesis rate for a set of protiens. One of these proteins, designated H35, is a prominent cellular protein present only during exponential growth. Reduction of H35 synthesis is transient and delayed following an IPTG pulse. Cellular response to an IPTG pulse during exponential growth shares several features with a heat shock response. Significant increases in the specific growth rate of cells in both amino-acid-supplemented minimal medium and complex medium were observed for some IPTG concentrations relative to IPTG-free cultures. Other IPTG concentrations caused a reduction in specific growth rate.Offprint requests to: J. E. Bailey     

‘Radicle' biochemistry: the biology of root-specific metabolism

The roots of higher plants are a fascinating and largely unexplored biological frontier. One of their features is the ability to synthesize a remarkable diversity of secondary metabolites, and to adjust their metabolic activities in response to biotic and abiotic stress. This includes the ability to exude a complex array of micro- and macromolecules into the rhizosphere, with the potential to affect the inter-relationships between plants and beneficial or deleterious soil-borne organisms. In the past, research on root biology has been hampered by the underground growth habit of roots and by the lack of a suitable experimental system. However, recent progess in growing roots in isolation has greatly facilitated the study of root-specific metabolism and contributed to our understanding of this remarkable plant organ.     

Phospholipids in the nucleus—metabolism and possible functions

Most of the phospholipids in the nuclear envelope are contained in the double nuclear membrane, and this has an active lipid metabolism consistent with its origins as a component of the endoplasmic reticular system. However, even after removal of the nuclear membrane with detergents, some phospholipids, mostly of unknown location and function, remain. Amongst these are all of the components of what appears to be a nuclear polyphosphoinositide signalling system, distinct from the well-established inositide pathway found in the plasma membrane. The consequences for nuclear function of the activation of these two inositide pathways are discussed, with a detailed consideration of proposed intranuclear functions for protein kinase C, and the maintenance of nuclear Ca²⁺ homoeostasis.     

Effect of α-p-chlorophenoxyisobutyrate on the metabolism of isoprenoid compounds in the rat

1. Feeding of alpha-p-chlorophenoxyisobutyrate (CPIB) to rats increased ubiquinone concentration in the liver but not in other tissues. The increase was progressive with the time of feeding and related to the concentration of CPIB in the diet. 2. Incorporation of [1-(14)C]acetate, but not of [2-(14)C]mevalonate, into sterols in the liver in vivo or by liver slices in vitro was decreased on feeding the rats with CPIB. However, incorporation of mevalonate into ubiquinone increased. 3. CPIB, when added in low concentrations to liver slices, had no effect on isoprene synthesis from acetate; higher concentrations, however, were inhibitory. 4. No activation of ubiquinone synthesis from mevalonate was observed when CPIB was added to the liver slices synthesizing ubiquinone. 5. The increase in ubiquinone in CPIB-fed animals appears to be due to increased synthesis in the initial stages and to decreased catabolism in the later stages. 6. An inverse relationship was found between the concentration of ubiquinone in the liver and the serum sterol concentration in CPIB-fed rats.     

Diacylglycerol kinase ζ controls diacylglycerol metabolism at the immunological synapse

Diacylglycerol (DAG) generation at the T cell immunological synapse (IS) determines the correct activation of antigen-specific immune responses. DAG kinases (DGKs) α and ζ act as negative regulators of DAG-mediated signals by catalyzing DAG conversion to phosphatidic acid (PA). Nonetheless, the specific input of each enzyme and their spatial regulation during IS formation remain uncharacterized. Here we report recruitment of endogenous DGKα and DGKζ to the T cell receptor (TCR) complex following TCR/CD28 engagement. Specific DGK gene silencing shows that PA production at the activated complex depends mainly on DGKζ, indicating functional differences between these proteins. DGKζ kinase activity at the TCR is enhanced by phorbol-12-myristate-13-acetate cotreatment, suggesting DAG-mediated regulation of DGKζ responsiveness. We used GFP-DGKζ and -DGKα chimeras to assess translocation dynamics during IS formation. Only GFP-DGKζ translocated rapidly to the plasma membrane at early stages of IS formation, independent of enzyme activity. Finally, use of a fluorescent DAG sensor confirmed rapid, sustained DAG accumulation at the IS and allowed us to directly correlate membrane translocation of active DGKζ with DAG consumption at the IS. This study highlights a DGKζ-specific function for local DAG metabolism at the IS and offers new clues to its mode of regulation.     

Anaerobic energy metabolism in the oligochaeteLumbriculus variegatus Müller

Summary Anoxia tolerance, glycogen degradation, free amino acid pool, adenylate energy charge and the accumulation and excretion of end products were monitored inLumbriculus variegatus Müller throughout 48 h of anoxia. A transition period lasting about 4 h could be distinguished from subsequent events during which malate, present in high amounts in the resting animals, is utilized, probably by conversion to succinate. Up to the 12th hour of anoxia there is an increase in concentration of free amino acids, except aspartate. Glutamate increases rapidly during the first half hour but decreases thereafter. Beginning with the second hour of anoxia the alanine concentration increases at the same rate glutamate concentration decreases, but the source of nitrogen during the first hour is unknown. It is argued that the nitrogen required for the synthesis of some of the amino acids is ultimately derived from proteolysis. After about 3 h of anoxia propionate and acetate are synthesized. At first these acids accumulate in the tissues, but after 4–6 h they are excreted into the surrounding medium. Acetate is excreted over the whole experimental period at a constant rate, whereas the excretion rate of propionate decreases slowly with time. The propionate/acetate ratio is in excess of 2. Classic malate dismutation is by far the most important mechanism in the maintenance of redox balance. Depletion of glycogen stores appears to play an important role in determining anoxic survival time. Due to extremely low activity of PEPCK the ratio of the specific activities of PK and PEPCK is very high. Further, the kinetic properties of pyruvate kinase do not support the assumption of a shift of the glycolytic carbon flow at the PEP level.Abbreviations PK Pyruvate kinase - PEPCK phosphoenolpyruvate carboxykinase - PEP phospho(enol)pyruvate - FBP fructose-1,6-bisphosphate - AEC adenylate energy charge - EMP-scheme Embden-Meyerhof-Parnas scheme of glycolysis - f _w fresh body weight - dw dry body weight     

Are polyamines involved in the induction and regulation of the Crassulacean acid metabolism?

Leaves of plants with Crassulacean acid metabolism (CAM) were analyzed for variation in the content of polyamines in connection with the metabolism of malic acid in the dark and in the light, and with the induction of full-CAM activity. Under conditions (long days) resulting in extremely low CAM activity, young leaves of K. blossfeldiana have very low content in the polyamine-precursor arginine and in putrescine. The content in these two substances was increased dramatically by full-CAM induction with short days. During the course of the night/day cycle two peaks of putrescine content were observed in leaves of Kalanchoe blossfeldiana Poelln. Tom Thumb performing full-CAM operation: a large increase occurs toward the end of the day and the first half of the night, and its kinetics corresponds to the increase in the rate of malic acid synthesis; another peak, very sharp, appears during the first hours of the day, concomitant with the time of release of malic acid from the vacuole into the cytoplasm. In the case of Bryophyllum daigremontianum Berger similar variations were observed for the content in spermidine. These results support the hypothesis that polyamines could be involved in countering the tendency toward acidification of the cytoplasm at those moments of CAM operation at which the local concentration of malic acid is increased (i.e., during active synthesis in the dark and during the efflux from the vacuole in the light).Abbreviation CAM Crassulacean acid metabolism     

The terrestrial evolution of metabolism and life – by the numbers

Background  

Allometric scaling relating body mass to metabolic rate by an exponent of the former (Kleiber's Law), commonly known as quarter-power scaling (QPS), is controversial for claims made on its behalf, especially that of its universality for all life. As originally formulated, Kleiber was based upon the study of heat; metabolic rate is quantified in watts (or calories per unit time). Techniques and technology for metabolic energy measurement have been refined but the math has not. QPS is susceptible to increasing deviations from theoretical predictions to data, suggesting that there is no single, universal exponent relevant to all of life. QPS's major proponents continue to fail to make good on hints of the power of the equation for understanding aging.     

Relation between the oxidation state of nicotinamide–adenine dinucleotide and the metabolism of spermatozoa

1. The existing procedures for extraction of oxidized and reduced nicotinamide coenzymes were adapted to spermatozoa to overcome the coenzyme-degrading activity of seminal plasma. 2. The content of total NAD(+) and NADH was determined in the spermatozoa of ram, bull, boar, stallion and cock. NADP(+) and NADPH were not detected in ram spermatozoa. 3. The oxidation state of sperm NAD depended on the seminal plasma, the removal of which produced a change in the percentage oxidation state of the coenzyme, 100x[NAD(+)/(NAD(+)+NADH)], without altering the total content of NAD(+)+NADH. 4. In suspensions of washed ram spermatozoa, incubated anaerobically at 25 degrees C, the percentage oxidation state of NAD declined with increasing spermatozoa concentration. 5. When ram or boar spermatozoa that had been previously washed and resuspended in Ringer phosphate medium, were incubated anaerobically at 25 degrees C with various substances, pronounced effects on the percentage oxidation state of NAD could be observed with l-lactate, pyruvate, oxaloacetate, dihydroxyacetone, formaldehyde and glyceraldehyde; sorbitol and acetoacetate acted only on ram spermatozoa; fructose, glucose, mannose and acetaldehyde acted predominantly on boar spermatozoa. Formaldehyde lowered the (NAD(+)+NADH) content of ram spermatozoa, but none of the other substances had a comparable effect. 6. The percentage oxidation state of sperm NAD was not influenced by exogenous cysteine, cystine, ergothioneine or ascorbate. 7. A highly active sorbitol dehydrogenase could be prepared from ram, but not from boar, spermatozoa. 8. Sorbitol, acetoacetate and 3-hydroxybutyrate effectively supported the respiration of ram, but not boar, spermatozoa. 9. ;Cold shock', resulting from sudden cooling of spermatozoa, abolished motility completely and irreversibly but produced only a slow and partial decrease in the total NAD content. Slight over-heating, sufficient to produce loss of motility, had no adverse effect on the total NAD content. 10. Storage of ram sperm at 14 degrees C produced only a small decrease of NAD after 2 days, but subsequently the loss became greater.