Proline transport and metabolism in Rickettsia prowazekii

Purified Rickettsia prowazekii cells were able to transport L-proline. The influx of this amino acid had a Kt of 14 microM and a Vmax of about 64 pmol/min per mg of protein. Proline could not be transported by heat-killed or metabolically poisoned rickettsiae or at 0 degrees C. The uptake of proline was linear for almost 2 h. More than 90% of the accumulated intracellular radioactivity was proline. This intracellular pool could not be chased out of the cell by excess non-radioactive proline and did not exit into a proline-free medium. These results indicate that intracellular proline was bound or that the cell had a very limited efflux component for proline transport. The influx of proline was specific: among various analogs tested, only 3,4-dehydro-D,L-proline was effective in inhibiting proline uptake. R. prowazekii cells were unable to utilize proline as an energy source to drive hemolysis, and no measurable evolution from the rickettsiae of CO2 derived from proline occurred. The activities of the enzymes pyrroline-5-carboxylate-reductase and pyrroline-5-carboxylate dehydrogenase were not detectable. These enzymes are important in anabolism and catabolism of proline, respectively, and, if present in R. prowazekii have activities less than 1% of those in Escherichia coli.     

Proline metabolism in sepsis

Summary Sepsis is characterized by an abnormal increase in plasma proline (PRO) level, which tends to be related to the severity of disease. This study has been performed to assess the relationship between changes in plasma PRO and levels and doses of other amino acids (AA) in critically ill septic patients undergoing total parenteral nutrition (TPN).Sixteen septic patients receiving TPN were randomly divided into two groups: 8 patients (Group A) received TPN with a standard AA solution, and 8 patients (Group B) with a modified AA solution (isonitrogenous, branchedchain AA enriched, with unchanged PRO concentration). Serial determinations of plasma AA profiles and of other variables were performed in each patient for a total of 396 measurements. In Group A mean plasma PRO level was 372M/L; changes in PRO were tightly correlated with changes in the levels of most of the other AA, and the highest PRO levels characterized the more severely unbalanced septic metabolic profiles. In Group B, plasma levels of PRO and of the other AA (except glutamate, aspartate, taurine and the three branched-chain AA) decreased. The decrease in PRO level was well correlated with the increased branched-chain AA dose and with simultaneous decreases in plasma lactate and respiratory quotient. These changes could be related to a specific effect of branched-chain AA on septic metabolic derangement and on PRO metabolism, and to an improved balance between protein synthesis and catabolism.     

Proline metabolism in the conceptus: implications for fetal growth and development

Although there are published studies of proline biochemistry and nutrition in cultured cells and postnatal animals, little is known about proline metabolism and function in the conceptus (embryo/fetus, associated placental membranes, and fetal fluids). Because of the invasive nature of biochemical research on placental and fetal growth, animal models are often used to test hypotheses of biological importance. Recent evidence from studies with pigs and sheep shows that proline is a major substrate for polyamine synthesis via proline oxidase, ornithine aminotransferase, and ornithine decarboxylase in placentae. Both porcine and ovine placentae have a high capacity for proline catabolism and polyamine production. In addition, allantoic and amniotic fluids contain enzymes to convert proline into ornithine, which is delivered through the circulation to placental tissues. There is exquisite metabolic coordination among integrated pathways that support highest rates of polyamine synthesis and concentrations in placentae during early gestation when placental growth is most rapid. Interestingly, reduced placental and fetal growth are associated with reductions in placental proline transport, proline oxidase activity, and concentrations of polyamines in gestating dams with either naturally occurring or malnutrition-induced growth retardation. Conversely, increasing proline availability in maternal plasma through nutritional or pharmacological modulation in pigs and sheep enhances concentrations of proline and polyamines in placentae and fetal fluids, as well as fetal growth. These novel findings suggest an important role for proline in conceptus metabolism, growth and development, as well as a potential treatment for intrauterine growth restriction, which is a significant problem in both human medicine and animal agriculture.     

Proline transport in rat liver mitochondria.

Proline transport across the inner membrane of rat liver mitochondria shows the following properties: (a) It is stereospecific; the penetration of l-proline is two times faster than the penetration of dl-proline. (b) Proline is accumulated against a concentration gradient, (c) The transport of proline is enhanced in the presence of respiratory substrates such as succinate or tetramethylphenylenediamine + ascorbate; it is inhibited by uncouplers of oxidative phosphorylation. (d) Proline transport is inhibited by mersalyl and p-chloromercuribenzoate, but not by hydrophobic thiol blocking reagents; thus, proline transport involves thiol groups located in a very hydrophilic environment. The penetration of several other neutral amino acids (alanine, glycine, serine) is almost insensitive to mersalyl. These results suggest that proline does not travel across the mitochondrial membrane by free diffusion, but that its transport is mediated by a specific carrier. The rate of proline transport has been compared with the rates of the first two steps of proline oxidation: All of these rates are very similar, indicating that proline transport is not a limiting factor of proline metabolism in rat liver mitochondria.     

Proline and valine transport in Agrobacterium tumefaciens C-58

Abstract The transport of proline and valine by Agrobacterium tumefaciens was investigated. Proline uptake by starved cells was found to be higher in the presence of glucose than in its absence. Valine uptake, on the other hand, was lowered in the presence of glucose. Proline uptake was found to be insensitive to the action of dicyclohexyl carbodiimide (DCCD), a membrane ATPase inhibitor, whereas valine uptake appeared to show some sensitivity to this agent. The results obtained seem to suggest that the two transport systems make use of different energy stores.     

Cell-to-cell transport of macromolecules during early plant development

Plant cells exchange developmental signals, distribute nutrients and ribonucleoprotein complexes through dynamic intercellular channels termed plasmodesmata (PD). Multidisciplinary investigations over the last decade have provided evidence that plasmodesmatal regulation is critical to various basic plant functions, such as development, host-pathogen interactions, and systemic RNA-silencing. This review highlights the cell-to-cell transport of micro- and macromolecules via PD during embryo and seedling growth.     

Altered sucrose metabolism impacts plant biomass production and flower development

Nicotiana tabacum (tobacco) was transformed with three genes involved in sucrose metabolism, UDP-glucose pyrophosphorylase (UGPase, EC 2.7.7.9), sucrose synthase (SuSy, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14). Plants harbouring the single transgenes were subsequently crossed to produce double and triple transgenic lines, including: 2 × 35S::UGPase × SPS, 4CL::UGPase × SPS, 2 × 35S::SuSy × SPS, 4CL::SuSy × SPS, 2 × 35S::UGPase × SuSy × SPS, and 4CL::UGPase × SuSy × SPS. The ultimate aim of the study was to examine whether it is possible to alter cellulose production through the manipulation of sucrose metabolism genes. While altering sucrose metabolism using UGPase, SuSy and SPS does not have an end effect on cellulose production, their simultaneous overexpression resulted in enhanced primary growth as seen in an increase in height growth, in some cases over 50%. Furthermore, the pyramiding strategy of simultaneously altering the expression of multiple genes in combination resulted in increased time to reproductive bud formation as well as altered flower morphology and foliar stipule formation in 4CL lines. Upregulation of these sucrose metabolism genes appears to directly impact primary growth and therefore biomass production in tobacco.     

Proline transport increases growth efficiency in salt-stressed Streptomyces griseus

Streptomyces griseus synthesizes proline for osmoregulation under salt stress. Uptake of exogenous [14C]proline and internal synthesis of proline were quantified in cells growing at salt concentrations from 0 to 1 M NaCl. Externally supplied proline accounted for an increased proportion of the intracellular pool of free proline as salt concentration was increased, but neither the concentration nor the composition of the internal amino acid pool was substantially altered by supply of exogenous proline. Uptake of exogenous proline significantly increased the specific growth yield of S. griseus growing under salt stress; the increased yield was proportional to reductions in proline synthesis.     

Proline transport increases growth efficiency in salt-stressed Streptomyces griseus.

Streptomyces griseus synthesizes proline for osmoregulation under salt stress. Uptake of exogenous [14C]proline and internal synthesis of proline were quantified in cells growing at salt concentrations from 0 to 1 M NaCl. Externally supplied proline accounted for an increased proportion of the intracellular pool of free proline as salt concentration was increased, but neither the concentration nor the composition of the internal amino acid pool was substantially altered by supply of exogenous proline. Uptake of exogenous proline significantly increased the specific growth yield of S. griseus growing under salt stress; the increased yield was proportional to reductions in proline synthesis.     

The function of metabolism in phosphorus accumulation in plant roots and its transport over long distances

The values of influx (Ji) and efflux (Jo) of phosphates through intact maize roots (primary, seed roots) have confirmed the dependence of the P concentration in nutrient medium on the activity and efficiency of transport mechanism with respect to the accumulation of phosphates (J) by roots. The phosphate accumulation is about 97–99 % of the total uptake. If the P concentration is < 1 mM the efflux is negligible, and Ji <=g Jo. In contrast, if the P concentration is τ 1 mM, the proportion of efflux significantly increases, up to 45 % of the whole influx. The approximation to the conditions of equilibrium of phosphate flows ( Ji = Jo) depends on the P concentration in root cells, the accumulation of phosphates being determined by the relation Ji τ Jo. In the roots growing in P-containing medium the values of efflux are much higher than in the roots lacking P. The positive effect of Ca²⁺ ions on the accumulation of phosphates is caused by the decreased proportion of efflux. The factors instigating the integrity or non-integrity of the cell structure (Ca²⁺, SDS, EDTA, Sorbitol,etc.) and thus its effectiveness determine the accumulation of phosphates by roots. Analogously, the factors stimulating the ability of accepted phosphate to be metabolized, and their use in the form of organic compounds decrease the proportion of efflux; these activities are shown in the increased efficiency of the phosphate uptake. The presented results show the importance of the integrity of the cell structure, the functioning of membranes and of metabolism efficiency for the accumulation of phosphates by plant roots. The main form of phosphorus transport in xylem exudate is inorganic phosphorus. Its share is from 79 to 82 % of the total amount of transported P. The utilization of P in the roots in the form of organic, slowly motabolizable P compounds (mannose-6-phosphate) and inhibition of acid phosphatase activity effectively restrains P transport over long distances. The correlation of P transport from roots into shoots with phosphatase activity was established (correlation coefficient is 0.74⁺⁺). It can be summarized that long-distance P tran sport is a function of dephosphorylating reactions.     

Cell-to-cell transport of proteins and fluorescent tracers via plasmodesmata during plant development

Plant cells communicate with each other via channels called plasmodesmata (PD). PD are not passive channels, but critical players in gene regulation, controlling intercellular transport of macromolecules between particular cells during development.