Energy metabolism in relation to oxygen partial pressure in human skeletal muscle during exercise.

1. The intramuscular oxygen partial pressure (pO2) in human gastrocnemius muscle was monitored during exercise and compared with metabolite concentrations reflecting the energy and the redox state in the tissue. Ten normal subjects and ten patients with peripheral vascular occlusive disease were investigated. 2. In normal subjects the pO2 at the end of exercise was related to the intensity of the exercise, expressed as effect (J/s) per contraction. 3. In both patients and normal subject the pO2 was related to the [ATP]/[ADP] ratio, the [lactate/[pyruvate] ratio and the phosphocreatine concentration in the muscle tissue at rest and during exercise. 4. At each pO2 value, a lower [lactate/[pyruvate] ratio was found in the muscle tissue of the patients compared with that of normal subjects. This was interpreted as a beneficial effect of the higher oxidative-enzyme capacity in the muscle of the patients. 5. The results show the importance of pO2 for the regulation of the energy and the redox state of the tissue. During exercise the changes induced in pO2 and thus the energy state will stimulate the respiratory rate. This might be an important link in triggering the oxidative-enzyme capacity in response to physical training as well as in peripheral vascular occlusive disease.     

Synthetic analogues of polynucleotides. (Part) XIV. The synthesis of poly (3''-0-carboxymethyl-2''-deoxycytidine) and its interaction with polyinosinic acid.

Poly (3'-O-carboxymethyl-2'-deoxyctidine) (VII) has been synthesised by the polymerisation of 3'-O-carboxymethyl-4-N-phenoxyacety-2'-deoxycytidine (V) and removal of the phenoxyacetyl groups under acidic conditions. V was obtained by the action of 2,4-dinitrophenyl phenylacetate on 3'-O-carboxymethyl-5'-O-triphenylmethyl-2'-deoxycytidine (III) followed by removal of the triphenylmethyl group under carefully controlled acidic conditions. The polymer, VII gave a hypochromic effect of about 20% at 250nm when mixed with poly (1) in 0.2Macetate, pH 5.0. It appeared, therefore, that a complex was formed. Upon heating a solution of this complex there was an initial decrease in optical density followed by a much larger increase to give a Tm of about 60 degrees. Attempts to form the 3'-O-carboxymethyl derivative of 4-N-phenoxyacetyl-5'-O-'triphenylmethyl-2'-deoxycytidine to give a shorter synthetic route to VII were not successful. 3'-O-Carboxymethyl-2'-deoxycytidine was obtained by removal of thetriphenylmethyl group from III. Attempts to polymerise this compound in concentrated aqueous solution with a water-soluble carbodiimide were not successful.     

Radiation injury in mouse lung: dependence on oxygen levels in the inspired gas

The relationship between radiosensitivity and the partial pressure of oxygen (PO2) in the inspired gas has been established for radiation pneumonitis as a measure of lung damage following irradiation of the mouse thorax. The radiosensitivity at low PO2 (0-1 per cent) fitted the linear transformation of the Alper, Howard-Flanders relationship giving a K value for lung tissue of 1.35 per cent oxygen with an oxygen enhancement ratio, m, of 2.13. The radiosensitivity at higher PO2 (5-21 per cent) did not fit the Alper, Howard-Flanders relationship probably because the PO2 of the inspired gas was greater than the PO2 in the alveolus. At the low PO2 levels in the inspired gas, back diffusion of oxygen from blood into the alveolus may lead to errors in the estimated value of K. If the low value of m is due to this 'contaminating' oxygen from blood then by taking a higher value for m, the amount of contaminating oxygen can be calculated (0.23 per cent) and a 'true' value for K(1.1 per cent) determined. Other uncertainties in this estimate of K due to the radiolytic consumption of oxygen and possible inadequacies in equilibration are discussed. Allowing for the uncertainties, it is concluded that the K value for lung damage lies towards the upper end of the range of K values measured for cells in vitro.     

Advancing Forest Cover Development on a High‐Elevation Sierra Nevada Mine Site with Nutritional Amendments

Selected nutrient amendments were evaluated for their capacity to enhance growth and nutrition of established but stunted Jeffrey pine (Pinus jeffreyi Grev. & Balf.) saplings on an acidic Sierra Nevada surface mine. The amendments were applied by topdressing at three rates each and consisted of Forestcote 22‐4‐6 + Minors, a controlled‐release formulation; Free Flow 29‐3‐4 and Hydro Agri 21‐7‐14, two conventional fertilizers, with the former featuring urea as the predominant N source, whereas that for the latter was exclusively ammoniacal and nitrate forms; and Milorganite 6‐2‐0 + Iron, an organic amendment based on municipal biosolids. All formulations reinvigorated sapling growth, generally more so as the amounts supplied increased, with the Free Flow and Hydro Agri amendments marginally more stimulative than Forestcote and Milorganite. Foliar analysis revealed that fertilized saplings had more N, with concentrations that generally rose with amounts supplied, and P but less Mn and Al than the control. Enhanced N nutrition in particular but also that of P probably accounted for most of the growth stimulation by the amendments, as availability of both in the soil was limiting. Of the two metallic elements, reduced Mn was likely most critical because concentrations encountered here were exceedingly elevated overall, including that in the soil, although soil Al was also high. These results suggest that a variety of nutritional amendments can be employed in forest restoration on surface mine sites and those similarly degraded, including sites for which dry climates greatly influence the selection of remedial practices.     

From Chlorella to chloroplasts: a personal note

An historical and personal reflection on the function of the Benson–Calvin Cycle in isolated chloroplasts, the role of inorganic phosphate and the manner in which this might be best presented to students.     

Phosphoenolpyruvate carboxykinase in Arabidopsis: changes in gene expression, protein and activity during vegetative and reproductive development

The aim of this work was to investigate the occurrence of phosphoenolpyruvate carboxykinase (PEPCK) in different tissues of Arabidopsis thaliana throughout its vegetative and reproductive growth. The A. thaliana genome contains two PEPCK genes (PCK1 and PCK2), and these are predicted to generate 73,404 and 72,891 Da protein products, respectively. Both genes were transcribed in a range of tissues; however, PCK1 mRNA appeared to be more abundant and was present in a wider range of tissues. PEPCK protein was present in flowers, fruit, developing seed, germinating seed, leaves, stems and roots. Two PEPCK polypeptides, of approximately 74 and approximately 73 kDa were detected by immunoblotting, and these may arise from PCK1 and PCK2, respectively. PEPCK was abundant in cotyledons during post-germinative growth, and this is consistent with its well established role in gluconeogenesis. PEPCK was also abundant in sink tissues, such as young leaves, in developing flowers, fruit and seed. Immunohistochemistry and in situ hybridization showed that PEPCK was present in the nectaries, stigma, endocarp of the fruit wall and in tissues involved in the transfer of assimilates to the developing ovules and seeds, such as the vasculature and seed coat. The potential functions of PEPCK in A. thaliana are discussed.     

Coordinate regulation of phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase by light and CO2 during C4 photosynthesis

The aim of this study was to investigate the relationship between the phosphorylation and activation states of phosphoenolpyruvate carboxykinase (PEPCK) and to investigate how the phosphorylation states of PEPCK and phosphoenolpyruvate carboxylase (PEPC) are coordinated in response to light intensity and CO(2) concentration during photosynthesis in leaves of the C(4) plant Guinea grass (Panicum maximum). There was a linear, reciprocal relationship between the phosphorylation state of PEPCK and its activation state, determined in a selective assay that distinguishes phosphorylated from nonphosphorylated forms of the enzyme. At high photon flux density and high CO(2) (750 microL L(-1)), PEPC was maximally phosphorylated and PEPCK maximally dephosphorylated within 1 h of illumination. The phosphorylation state of both enzymes did not saturate until high light intensities (about 1,400 micromol quanta m(-2) s(-1)) were reached. After illumination at lower light intensities and CO(2) concentrations, the overall change in phosphorylation state was smaller and it took longer for the change in phosphorylation state to occur. Phosphorylation states of PEPC and PEPCK showed a strikingly similar, but inverse, pattern in relation to changes in light and CO(2). The protein phosphatase inhibitor, okadaic acid, promoted the phosphorylation of both enzymes. The protein synthesis inhibitor, cycloheximide, blocked dark phosphorylation of PEPCK. The data show that PEPC and PEPCK phosphorylation states are closely coordinated in vivo, despite being located in the mesophyll and bundle sheath cells, respectively.     

The blood contains multiple distinct progenitor populations with clonogenic B and T lineage potential

The thymus is seeded by bone marrow-derived progenitors that circulate in the blood. Multiple cell types can be found in the thymus early after i.v. administration or in steady state, but most fail to satisfy the known characteristics of true T progenitors. Cells that do conform to classical definitions retain multilineage potential, but surprisingly, cannot make B cells. Because acquisition of the T lineage fate among noncommitted progenitors is a lengthy process, the absence of B cell potential in early thymocytes suggests that B and T lineages diverge prethymically. To test this suggestion, we screened numerous presumptive progenitor populations for T cell growth and differentiation potential, as well as for clonogenic T or B cell development. We find that blood and marrow each contain multiple distinct subsets that display growth and differentiation potential consistent with being canonical T progenitors. Assessment of clonogenic potential further shows that although all blood and marrow populations have high T cell cloning potential, no T/non-B cells are apparent. These data suggest that either true thymic reconstitution potential derives from a small T/non-B cell subset of one of these populations, or that most of the cells defined as canonical progenitors within the thymus do not, in fact, reside in the mainstream of T progenitor differentiation.     

Visual documentation of ovine pituitary gland development with magnetic resonance imaging following zeranol treatment

The objective of the current study was to determine whether magnetic resonance imaging (MRI) could be successfully utilized to document the effect of an oestrogenic anabolic agent on pituitary gland growth. The experimental animals consisted of two 1/2 sibling Suffolk wethers (castrated rams), which received either no implant (control, n = 1) or a 24 mg zeranol implant at day 0 and day 42 (zeranol; n = 1). Animals were anaesthetized with propofol and supported with oxygen during the MRI procedure. A mobile MRI unit with a 0.5 tesla (T), superconducting magnet was used to obtain 3 mm thick, non-contrast enhanced, T1-weighted (TR 500-600, TE25) sagittal, transverse and dorsal images of the pituitary gland. Sagittal images were recorded only when the mesencephalic aqueduct and infundibulum were distinctly visible in the same image. Pituitary glands were imaged at 14-day intervals for 70 days to determine if and when the anabolic effects of zeranol on pituitary gland growth could be visualized using MRI techniques. Three separate measurements of the pituitary gland dimensions made with the on-screen cursor were averaged to calculate pituitary gland dimensions and volume. A computer-assisted image analysis system and laser film images were used to determine pituitary gland area. Increases in pituitary gland volume for control and zeranol-treated animals were evident within 14 days, and by the end of the 70-day study, the increase in pituitary volume for the zeranol-treated animal was three times greater than that of the control animal. Overall, our results indicate that MRI technology can be successfully used to document the development of the pituitary gland in vivo. Application of knowledge gained from this novel approach to study the growth, development and function of endocrine glands over time, and within the same animal, will enhance human and animal endocrine diagnostic procedures.