Biomedical subjects

N E Tolbert

Publications and source records attributed to N E Tolbert.

At least 37 records · Page 2Linked to original sources

PubMed1988

Isolation of Intact Chloroplasts from Dunaliella tertiolecta.

Cells of Dunaliella tertiolecta from the log phase of growth were broken by rapid extrusion at low pressure through a Yeda press and the chloroplasts were isolated by centrifugation through a Percoll gradient. Osmolarity of the growth media, the suspending media, and the Percoll gradient was kept identical to minimize change in chloroplast volume and mitochondrial entrapment. The isolated intact chloroplasts were obtained in a 30 to 50% yield based on chlorophyll and were stable to washing with buffered medium. Isolated chloroplast yield and purity was dependent on cell culture condition; a cycle of 16 hours light and 8 hours dark with continuous high CO(2) was optimum. Isolated chloroplasts were about 90% intact by microscopic examination, ferricyanide-dependent O(2) evolution, and the distribution of four stromal enzymes. Enzymes associated with glycolate metabolism were not in the chloroplast fraction. The isolated chloroplasts with 10 millimolar bicarbonate evolved 24 micromoles of O(2) and fixed 21 micromoles of CO(2) per hour per milligram of chlorophyll, which rates were about one-third of those by whole cells. The inhibition of oxygen evolution by 10 millimolar phosphate was reversed by P-glycerate. Whole chloroplasts were also isolated from cells adapted to low CO(2) in air for 24 hours. On low CO(2) the cells excreted more gelatinous material, which had to be removed with additional washing of the cells, before it was possible to obtain good chloroplast preparations.

Journal Article↗

PubMed1988

Isolation of dihydroxyacetone phosphate reductase from dunaliella chloroplasts and comparison with isozymes from spinach leaves.

A dihydroxyacetone phosphate (DHAP) reductase has been isolated in 50% yield from Dunaliella tertiolecta by rapid chromatography on diethylaminoethyl cellulose. The activity was located in the chloroplasts. The enzyme was cold labile, but if stored with 2 molar glycerol, most of the activity was restored at 30 degrees C after 20 minutes. The spinach (Spinacia oleracea L.) reductase isoforms were not activated by heat treatment. Whereas the spinach chloroplast DHAP reductase isoform was stimulated by leaf thioredoxin, the enzyme from Dunaliella was stimulated by reduced Escherichia coli thioredoxin. The reductase from Dunaliella was insensitive to surfactants, whereas the higher plant reductases were completely inhibited by traces of detergents. The partially purified, cold-inactivated reductase from Dunaliella was reactivated and stimulated by 25 millimolar Mg(2+) or by 250 millimolar salts, such as NaCl or KCl, which inhibited the spinach chloroplast enzyme. Phosphate at 3 to 10 millimolar severely inhibited the algal enzyme, whereas phosphate stimulated the isoform in spinach chloroplasts. Phosphate inhibition of the algal reductase was partially reversed by the addition of NaCl or MgCl(2) and totally by both. In the presence of 10 millimolar phosphate, 25 millimolar MgCl(2), and 100 millimolar NaCl, reduced thioredoxin causes a further twofold stimulation of the algal enzyme. The Dunaliella reductase utilized either NADH or NADPH with the same pH maximum at about 7.0. The apparent K(m) (NADH) was 74 micromolar and K(m) (NADPH) was 81 micromolar. Apparent V(max) was 1100 mumoles DHAP reduced per hour per milligram chlorophyll for NADH, but due to NADH inhibition highest measured values were 350 to 400. The DHAP reductase from spinach chloroplasts exhibited little activity with NADPH above pH 7.0. Thus, the spinach chloroplast enzyme appears to use NADH in vivo, whereas the chloroplast enzyme from Dunaliella or the cytosolic isozyme from spinach may utilize either nucleotide.

Journal Article↗

PubMed1987

NADH:hydroxypyruvate reductase and NADPH:glyoxylate reductase in algae: partial purification and characterization from Chlamydomonas reinhardtii.

Hydroxypyruvate and glyoxylate reductase activities were measured in extracts from the unicellular green algae, Chlamydomonas reinhardtii, Chlorella vulgaris, Chlorella miniata, and Dunaliella tertiolecta. Only trace levels of these activities were detectable in the blue-green algae, Anabaena variabilis and Synechococcus leopoliensis. A NADH-dependent hydroxypyruvate reductase was purified 130-fold from Chlamydomonas to a specific activity of 18 mumol NADH oxidized X min-1 X mg protein-1. The pH optimum was 5.0 to 7.0 in the presence of phosphate and the Km(hydroxypyruvate) was 0.05 mM. Substrate inhibition by hydroxypyruvate could be partially relieved by phosphate. The molecular weight, estimated by gel filtration, was 96,000. NADH-dependent glyoxylate reductase activity copurified with the hydroxypyruvate reductase. The Km(glyoxylate) was 10 mM, and the pH optimum was 4.5 to 8.5. A specific NADPH:glyoxylate reductase was also partially purified which did not reduce hydroxypyruvate or pyruvate. The NADPH:glyoxylate reductase had a Km(glyoxylate) of 0.1 mM and a pH optimum of 5.0 to 9.5. These reductases were compared with the pyruvate reductase of Chlamydomonas which also catalyzes the reduction of both hydroxypyruvate and glyoxylate.

Alcohol Oxidoreductases↗

PubMed1987

Inhibition of glycolate and D-lactate metabolism in a Chlamydomonas reinhardtii mutant deficient in mitochondrial respiration.

The possibility that glycolate oxidation in unicellular green algae is linked to mitochondrial electron transport, rather than to peroxisomal metabolism as in higher plants and animals, was studied in a mutant of Chlamydomonas reinhardtii (dk97) deficient in cytochrome oxidase. This mutant had normal rates of dark respiration (40 +/- 15 mumol of O(2) uptake per hr per mg of chlorophyll) but had only 11% of wild-type levels of cytochrome oxidase activity. Salicylhydroxamic acid (SHAM) reduced the dark respiration rate of dk97 cells by 71%, but cyanide did not significantly inhibit this rate. During photosynthesis in the presence of SHAM, glycolate oxidation was blocked, resulting in glycolate accumulation and excretion by mutant cells but not by wild-type Chlamydomonas. D-Lactate, which accumulated after brief periods of anaerobiosis in Chlamydomonas, was reoxidized by air-grown cells only aerobically in the light, and reoxidation of D-lactate was blocked by SHAM in the dk97 cells. Thus, glycolate and D-lactate dehydrogenase activities are both linked to mitochondrial electron transport in Chlamydomonas. During photosynthetic (14)CO(2) fixation by dk97 cells in the presence of SHAM, (14)C-labeled tricarboxylic acid cycle intermediates accumulated, indicating that, in Chlamydomonas, mitochondrial respiration functions during photosynthesis.

Journal Article↗

PubMed1987

Evidence for Inorganic Carbon Transport by Intact Chloroplasts of Chlamydomonas reinhardtii.

Isolated intact chloroplasts from wall-less mutants of Chlamydomonas reinhardtii accumulate inorganic carbon (C(i)) from the medium provided the cells had been adapted to low CO(2) photoautotrophic growth conditions. Chloroplasts from cultures grown on high (5%) CO(2) or photoheterotrophically with acetate did not accumulate inorganic carbon. Chloroplast C(i) accumulation from low CO(2) grown cells was light dependent and was inhibited by uncouplers and inhibitors of electron transport. In a model for C(i) accumulation by Chlamydomonas, it is proposed that CO(2) diffuses into the cell and C(i) accumulation occurs in the chloroplast.

Journal Article↗

PubMed1987

Evidence That an Internal Carbonic Anhydrase Is Present in 5% CO(2)-Grown and Air-Grown Chlamydomonas.

Inorganic carbon (C(i)) uptake was measured in wild-type cells of Chlamydomonas reinhardtii, and in cia-3, a mutant strain of C. reinhardtii that cannot grow with air levels of CO(2). Both air-grown cells, that have a CO(2) concentrating system, and 5% CO(2)-grown cells that do not have this system, were used. When the external pH was 5.1 or 7.3, air-grown, wild-type cells accumulated inorganic carbon (C(i)) and this accumulation was enhanced when the permeant carbonic anhydrase inhibitor, ethoxyzolamide, was added. When the external pH was 5.1, 5% CO(2)-grown cells also accumulated some C(i), although not as much as air-grown cells and this accumulation was stimulated by the addition of ethoxyzolamide. At the same time, ethoxyzolamide inhibited CO(2) fixation by high CO(2)-grown, wild-type cells at both pH 5.1 and 7.3. These observations imply that 5% CO(2)-grown, wild-type cells, have a physiologically important internal carbonic anhydrase, although the major carbonic anhydrase located in the periplasmic space is only present in air-grown cells. Inorganic carbon uptake by cia-3 cells supported this conclusion. This mutant strain, which is thought to lack an internal carbonic anhydrase, was unaffected by ethoxyzolamide at pH 5.1. Other physiological characteristics of cia-3 resemble those of wild-type cells that have been treated with ethoxyzolamide. It is concluded that an internal carbonic anhydrase is under different regulatory control than the periplasmic carbonic anhydrase.

Journal Article↗

PubMed1986

Effect of Osmotic Stress on Carbon Metabolism in Chlamydomonas reinhardtii: Accumulation of Glycerol as an Osmoregulatory Solute.

NaCl, KCl, and sucrose at equiosmolar concentrations had similar inhibitory effects on photosynthetic carbon metabolism by the freshwater green alga, Chlamydomonas reinhardtii. Inhibitory concentrations of these solutes altered the products of photosynthetic (14)CO(2) incorporation, resulting in reduced incorporation into starch, sugar phosphates, lactate, and glycolate, but caused an accumulation of glycerol both intracellularly and in the medium.

Journal Article↗

PubMed1986

Glycolate Metabolism and Excretion by Chlamydomonas reinhardtii.

The flux of glycolate through the C(2) pathway in Chlamydomonas reinhardtii was estimated after inhibition of the pathway with aminooxyacetate (AOA) or aminoacetonitrile (AAN) by measurement of the accumulation of glycolate and glycine. Cells grown photoautotrophically in air excreted little glycolate except in the presence of 2 mm AOA when they excreted 5 micromoles glycolate per hour per milligram clorophyll. Cells grown on high CO(2) (1-5%) when transferred to air produced three times as much glycolate, with half of the glycolate metabolized and half excreted. The lower amount of glycolate produced by the air-grown cells reflects the presence of a CO(2) concentrating mechanism which raises the internal CO(2) level and decreases the ribulose-1,5-bisP oxygenase reaction for glycolate production. Despite the presence of the CO(2) concentrating mechanism, there was still a significant amount of glycolate produced and metabolized by air-grown Chlamydomonas. The capacity of these cells to metabolize between 5 and 10 micromoles of glycolate per hour per milligram chlorophyll was confirmed by measuring the biphasic uptake of added labeled glycolate. The initial rapid (<10 seconds) phase represented uptake of glycolate; the slow phase represented the metabolism of glycolate. The rates of glycolate metabolism were in agreement with those determined using the C(2)-cycle inhibitors during CO(2) fixation.

Journal Article↗

PubMed1985

Inhibition and stimulation of ribulose-1,5-bisphosphate carboxylase/oxygenase by glyoxylate.

Glyoxylate is a slowly reversible inhibitor of the CO2/Mg2+-activated form of ribulose-1,5-bisphosphate carboxylase/oxygenase from spinach leaves. Inactivation occurred with an apparent dissociation constant of 3.3 mM and a maximum pseudo-first-order rate constant of 7 X 10(-3) s-1. The rate constant for reactivation was 1.2 X 10(-2) s-1. Glyoxylate did not cause differential inhibition of ribulosebisphosphate carboxylase or oxygenase activities. 6-Phosphogluconate protected the enzyme from inactivation by glyoxylate. Glyoxylate was incorporated irreversibly into the large subunit of ribulosebisphosphate carboxylase after reduction with sodium borohydride. Activated enzyme incorporated 1.3 mol of glyoxylate per mole protomer, while enzyme treated with carboxyarabinitol 1,5-bisphosphate (CABP) to protect the active sites incorporated only 0.3 mol glyoxylate per mole protomer. The data suggest that glyoxylate forms a Schiff base with a lysyl residue in the region of the catalytic site. Glyoxylate stimulated the activity of the unactivated enzyme by about twofold. Pseudo-first-order inactivation also occurred with the unactivated enzyme after the initial stimulation by glyoxylate, although at a much slower rate than with the activated enzyme. Glyoxylate treatment of partially activated enzyme did not stimulate formation of the quaternary complex of enzyme X CO2 X Mg2+ X CABP.

Enzyme Activation↗

PubMed1985

Characterization of an active-site peptide modified by glyoxylate and pyridoxal phosphate from spinach ribulosebisphosphate carboxylase/oxygenase.

Activated ribulosebisphosphate carboxylase/oxygenase from spinach was treated with glyoxylate plus or minus the transition-state analog, carboxyarabinitol bisphosphate, or the inactive enzyme with pyridoxal phosphate plus or minus the substrate, ribulose bisphosphate. Covalently modified adducts with glyoxylate or pyridoxal phosphate were formed following reduction with sodium borohydride. The derivatized enzymes were carboxymethylated and digested with trypsin; the labeled peptides which were unique to the unprotected samples were purified by ion-exchange chromatography and gel filtration. Both glyoxylate and pyridoxal phosphate were associated with only one major peptide, which in each case was subjected to amino acid analysis and sequencing. The sequence was -Tyr-Gly-Arg-Pro-Leu-Leu-Gly-Cys(Cm)-Thr-Ile-Lys-Lys*-Pro-Lys-, with both reagents exhibiting specificity for the same lysine residue as indicated by the asterisk. This peptide is identical to that previously isolated from spinach carboxylase labeled with either of two different phosphorylated affinity reagents and homologous to one from Rhodospirillum rubrum carboxylase modified by pyridoxal phosphate. The species invariance of this lysine residue, number 175, and the substantial conservation of adjacent sequence support the probability for a functional role in catalysis of the lysyl epsilon-amino group.

Amino Acid Sequence↗

PubMed1985

Inorganic Carbon Uptake by Chlamydomonas reinhardtii.

The rates of CO(2)-dependent O(2) evolution by Chlamydomonas reinhardtii, grown with either air levels of CO(2) or air with 5% CO(2), were measured at varying external pH. Over a pH range of 4.5 to 8.5, the external concentration of CO(2) required for half-maximal rates of photosynthesis was constant, averaging 25 micromolar for cells grown with 5% CO(2). This is consistent with the hypothesis that these cells take up CO(2) but not HCO(3) (-) from the medium and that their CO(2) requirement for photosynthesis reflects the K(m)(CO(2)) of ribulose bisphosphate carboxylase. Over a pH range of 4.5 to 9.5, cells grown with air required an external CO(2) concentration of only 0.4 to 3 micromolar for half-maximal rates of photosynthesis, consistent with a mechanism to accumulate external inorganic carbon in these cells. Air-grown cells can utilize external inorganic carbon efficiently even at pH 4.5 where the HCO(3) (-) concentration is very low (40 nanomolar). However, at high external pH, where HCO(3) (-) predominates, these cells cannot accumulate inorganic carbon as efficiently and require higher concentrations of NaHCO(3) to maintain their photosynthetic activity. These results imply that, at the plasma membrane, CO(2) is the permeant inorganic carbon species in air-grown cells as well as in cells grown on 5% CO(2). If active HCO(3) (-) accumulation is a step in CO(2) concentration by air-grown Chlamydomonas, it probably takes place in internal compartments of the cell and not at the plasmalemma.

Journal Article↗

PubMed1985

Anaerobic Formation of d-Lactate and Partial Purification and Characterization of a Pyruvate Reductase from Chlamydomonas reinhardtii.

d-Lactate accumulation in Chlamydomonas reinhardtii was dependent on anaerobic conditions. As much as 50% of the (14)C after 2 minutes of photosynthetic (14)CO(2) fixation moved into d-lactate from sugar phosphates if the cells became anaerobic for short time periods. No lactate accumulated in the dark until the O(2) concentration decreased to less than 0.1%. Lactate was determined to be of the d-configuration using stereospecific lactate dehydrogenases. d-Lactate produced anaerobically by algae grown on 5% CO(2) was only slowly metabolized aerobically in the light or dark, and in the dark, only a trace of the lactate was excreted.A pyruvate reductase (d-lactate: diphosphopyridine nucleotide oxidoreductase, EC 1.1.1.28) was partially purified 47-fold from Chlamydomonas. Because this enzyme catalyzes an essentially irreversible reaction in the direction of pyruvate reduction, it is considered to be a pyruvate reductase. The reductase activity in extracts of Chlamydomonas was 30 micromoles per hour per milligram chlorophyll. For the partially purified enzyme, the apparent K(m) (pyruvate) was 0.5 millimolar, and the pH optimum was 7.0. Studies with cycloheximide and chloramphenicol indicated that the enzyme was constitutive in aerobic cells. Potassium phosphate stimulated the reductase, and high salt and dithiothreitol were required for stability. The enzyme demonstrated substrate inhibition and was inhibited by ATP. Pyruvate reductase was separated from a hydroxypyruvate reductase by gel filtration chromatography, indicating the presence of separate reductases for these two substrates in Chlamydomonas.

Journal Article↗

PubMed1985

Effect of Carbonic Anhydrase Inhibitors on Inorganic Carbon Accumulation by Chlamydomonas reinhardtii.

Membrane-permeable and impermeable inhibitors of carbonic anhydrase have been used to assess the roles of extracellular and intracellular carbonic anhydrase on the inorganic carbon concentrating system in Chlamydomonas reinhardtii. Acetazolamide, ethoxzolamide, and a membrane-impermeable, dextran-bound sulfonamide were potent inhibitors of extracellular carbonic anhydrase measured with intact cells. At pH 5.1, where CO(2) is the predominant species of inorganic carbon, both acetazolamide and the dextran-bound sulfonamide had no effect on the concentration of CO(2) required for the half-maximal rate of photosynthetic O(2) evolution (K(0.5)[CO(2)]) or inorganic carbon accumulation. However, a more permeable inhibitor, ethoxzolamide, inhibited CO(2) fixation but increased the accumulation of inorganic carbon as compared with untreated cells. At pH 8, the K(0.5)(CO(2)) was increased from 0.6 micromolar to about 2 to 3 micromolar with both acetazolamide and the dextran-bound sulfonamide, but to a higher value of 60 micromolar with ethoxzolamide. These results are consistent with the hypothesis that CO(2) is the species of inorganic carbon which crosses the plasmalemma and that extracellular carbonic anhydrase is required to replenish CO(2) from HCO(3) (-) at high pH. These data also implicate a role for intracellular carbonic anhydrase in the inorganic carbon accumulating system, and indicate that both acetazolamide and the dextran-bound sulfonamide inhibit only the extracellular enzyme. It is suggested that HCO(3) (-) transport for internal accumulation might occur at the level of the chloroplast envelope.

Journal Article↗

PubMed1985

Effect of Triacontanol on Chlamydomonas: I. Stimulation of Growth and Photosynthetic CO(2) Assimilation.

Treatment of Chlamydomonas reinhardtii cells, cultured at 5% CO(2), with 1 to 1000 micrograms triacontanol (TRIA) per liter resulted in 21 to 35% increases in cell density, 7 to 31% increases in total chlorophyll, and 20 to 100% increases in photosynthetic CO(2) assimilation. The increase in CO(2) fixation with TRIA treatment occurred before, and was independent of, increases in total chlorophyll or cell number. Chlamydomonas cells responded to a broad range of TRIA concentrations that were at least one order of magnitude above the optimum concentration established for higher plants. The necessity for larger concentrations of TRIA may be due to destabilizing effects of Ca(2+) and K(+) present in the Chlamydomonas growth medium. These ions caused flocculation of the colloidally dispersed TRIA in apparent competition with binding of [(14)C]TRIA to Chlamydomonas cells. Octacosanol inhibited the effect of TRIA on photosynthetic CO(2) assimilation. TRIA treatment did not alter the distribution of (14)C-label among photosynthetic products. The effect of TRIA on photosynthetic CO(2) assimilation increased with time after treatment up to 3 days. Chlamydomonas cells that had been grown at low-CO(2) (air) did not respond to TRIA, and transfer of high-CO(2) (5%) grown cells that had responded to TRIA to a low-CO(2) atmosphere resulted in a loss of the effect of TRIA. The effect of pH on photosynthetic CO(2) assimilation indicated that CO(2) is probably the species of inorganic carbon utilized by control and TRIA-treated Chlamydomonas cells.

Journal Article↗

PubMed1985

Effect of Triacontanol on Chlamydomonas: II. Specific Activity of Ribulose-Bisphosphate Carboxylase/Oxygenase, Ribulose-Bisphosphate Concentration, and Characteristics of Photorespiration.

Increased photosynthetic CO(2) assimilation by Chlamydomonas reinhardtii cells treated with triacontanol (TRIA) was not due to changes in glycolate excretion, CO(2) compensation point, or the sensitivity of photosynthetic CO(2) assimilation to O(2). Kinetic analysis of TRIA-treated cells showed that the increase in photosynthetic CO(2) assimilation was a result of an increase in the apparent V(max) for intact cells. The total activity of ribulose-P(2) carboxylase/oxygenase was higher in cell lysates from TRIA-treated cells. However quantification of this enzyme concentration by binding of [(14)C]carboxyarabinitol-P(2) did not show an increase in TRIA-treated cells. Thus, there was an increase in the specific activity of ribulose-P(2) carboxylase/oxygenase extracted from Chlamydomonas cells treated with TRIA. TRIA alone had no effect on the activity of the enzyme in cell lysates from Chlamydomonas or purified from spinach (Spinacia oleracea L.) leaves.The ribulose-P(2) pool was 50 to 60% higher in cells treated with TRIA that were assayed for photosynthetic CO(2) assimilation at high- and low-CO(2). TRIA also increased ribulose-P(2) levels in the absence of CO(2) in the light with atmospheres of N(2) or N(2) with 21% O(2).

Journal Article↗

PubMed1985

Properties of Phosphoglycolate Phosphatase from Chlamydomonas reinhardtii and Anacystis nidulans.

The levels of activity of 2-phosphoglycolate phosphatase in the green algae, Chlamydomonas reinhardtii and Chlorella vulgaris, were in the range of 37 to 60 micromoles per milligram chlorophyll per hour and in the blue-green algae, Anacystis nidulans and Anabaena variabilis were 204 to 310 micromoles per milligram chlorophyll per hour. The activity in each species was similar regardless of whether the algae were grown with air or 5% CO(2) in air. The enzyme purified 530-fold from Chlamydomonas was stable, had a broad pH optimum between 6 and 8.5, and was specific for the hydrolysis of P-glycolate with a K(m) of 23 micromolar. The enzyme purified 18-fold from Anacystis was labile, had a sharp pH optimum at 6.3, and was also specific for P-glycolate with a K(m) of 94 micromolar. The molecular weight of the enzyme from Chlamydomonas was estimated to be 92,000 by gel filtration.The phosphatase from both sources required a divalent cation for activity. The Chlamydomonas enzyme was most effectively activated by Co(2+), but was also activated by Mg(2+) (K(a) = 30 micromolar), Mn(2+), and Zn(2+). The Anacystis enzyme was most effectively activated by Mg(2+) (K(a) = 140 micromolar), and was also activated by Co(2+) and Mn(2+), but not by Zn(2+). Anions were also required for maximum activity of the enzyme from both sources. The Chlamydomonas enzyme was activated about 2- to 3-fold by chloride (K(a) = 140 micromolar), bromide, nitrate, bicarbonate (K(a) = 600 micromolar) and formate. The Anacystis enzyme was activated over 10-fold by chloride (K(a) = 870 micromolar), bromide, iodide, and nitrate, but was not activated by bicarbonate or formate.The properties of the algal enzymes were similar to those previously reported for higher plants. The levels and kinetic properties of the enzyme seemed sufficient to account for the flux through the glycolate pathway that occurs in these algae. The phosphatase was not associated with the ribulose 1,5-bisphosphate carboxylase/oxygenase responsible for P-glycolate formation in the carboxysomes of Anacystis.

Journal Article↗

PubMed1984

Anion and divalent cation activation of phosphoglycolate phosphatase from leaves.

Phosphoglycolate (P-glycolate) phosphatase was purified 223-fold from spinach leaves by (NH4)2SO4 fractionation, DEAE-cellulose chromatography, and Sephadex G-200 chromatography. The partially purified enzyme had a broad pH optimum between 5.6 and 8.0 and was specific for the hydrolysis of P-glycolate with a Km (P-glycolate) of 26 microM. The enzyme was activated by divalent cations including Mg2+, Co2+, Mn2+, and Zn2+, and by anions including Cl-, Br-, NO-3, and HCOO-. Neither anions nor divalent cations activated the enzyme without the other. The P-glycolate phosphatase activities from tobacco leaves or the green algae, Chlamydomonas reinhardtii, also required Mg2+ and were activated by chloride. In addition, the enzyme was allosterically inhibited by ribose 5-phosphate. The activation of P-glycolate phosphatase by both anions and divalent cations and the inhibition by ribose 5-phosphate may be involved in the in vivo regulation of P-glycolate phosphatase activity.

Anions↗

PubMed1984

Effects of Chemical Treatments upon Photosynthetic Parameters in Soybean Seedlings.

The effects of various chemical treatments upon photosynthesis, soluble leaf protein, CO(2) compensation point, and leaf light transmission in soybean, Glycine max (L.) Merr., seedlings were examined following varying response periods after application at 14 to 17 days postemergence. The compounds N(6)-benzyladenine (BA), 2-(4-chlorophenoxy)-2-methylpropanoic acid (CPMP), (4-chlorophenoxy)acetic acid (CPA), rhodanine-N-acetic acid (RAA), and 2,3,5-triiodobenzoic acid (TIBA) significantly increased soluble protein and decreased senescence, measured by leaf light transmission, at CO(2) concentrations below the compensation point in a survival chamber. All compounds except BA significantly decreased transmission values under ambient atmospheric conditions. In statistically significant experiments, applications of 3.49 millimolar CPMP increased net photosynthesis on a leaf area basis by an average of 14.4% at all trifoliolate positions with increases generally requiring response periods of 12 days or longer. RAA at 1.31 and 2.61 millimolar increased net photosynthesis by 19 to 36% following 13-day response periods. CPMP and other compounds tested had no effect upon the CO(2) compensation point after 4- to 8-day response periods. The effects of CPMP and RAA upon net photosynthesis and soluble protein appeared to involve a combined stimulation of protein synthesis and an antisenescent effect. There were no indications that any of the photosynthetic changes observed resulted from direct differential effects upon ribulose bisphosphate carboxylase-oxygenase. The assays for soluble protein and light transmission responded more consistently to the chemicals than did photosynthesis.

Journal Article↗