Interaction of thymic peptide thymosinα 1 with vasoactive intestinal peptide (VIP) receptors

Thymic peptide thymosin ₁ (10^–9 to 3 x 1010^–7 M) is shown to inhibit the specific binding of [¹²⁵I]VIP to rat blood mononuclear cells and liver plasma membranes. Thymosin ₁ was 160 and 6250 times less potent that VIP at inhibiting [¹²⁵I]VIP binding to blood mononuclear cells and liver plasma membranes, respectively. Thymosin ₁ (10^–10 to 1010^–7 M) was weak in stimulating adenylate cyclase activity. Its efficacy is about 25 % and 27 % that of native VIP in blood mononuclear cells and liver plasma membranes, respectively. Thymosin ₁ may behave as a partial VIP agonist in rat.Abbreviations GRF growth hormone releasing factor - PHI porcine intestinal peptide having N-terminal histidine and C-terminal isoleucine amide - GIP gastric inhibitory polypeptide - VIP vasoactive intestinal peptide     

Functional and structural characterization of the secretin receptors in rat gastric glands: Desensitization and glycoprotein nature

We have documented and characterized the down-regulation of the¹²⁵I-secretin binding sites and the associated desensitization of the secretin receptor-cAMP system in rat gastric glands. Secretin induced a rapid decrease of the high-affinity¹²⁵I-secretin binding sites with t^1/2=30 min at 37°C. Half-maximal down-regulation and desensitization occurred at 10^–9 M secretin, a physiological concentration corresponding to the half-maximal activation of the secretin receptor. The Scatchard parameters of the low-affinity¹²⁵I-secretin binding sites were unaffected by the pretreatment. This desensitization is heterologous in view of the loss of responsiveness to the truncated glucagon-like peptide 1 (TGLP-1), and pharmacologically selective since the sectetin-related analogue VIP (10^–7 M) does not alter the secretin-induced cAMP generation in rat gastric glands. The glycoprotein nature of the secretin receptor has also been demonstrated using WGA-agarose affinity chromatography of the solubilized¹²⁵I-secretin receptor complex.     

Cyclic AMP-stimulating effect of vasoactive intestinal peptide in isolated epithelial cells of rat ventral prostate

Vasoactive intestinal peptide (VIP) has been shown to increase cyclic AMP content in isolated epithelial cells of rat ventral prostate. The stimulatory effect of VIP was dependent on time and temperature and was potentiated by a phosphodiesterase inhibitor. At 15°C, the response occurred in the 1·10⁻¹⁰−10⁻⁷ M range of VIP concentrations. Half-maximal stimulation of cellular cyclic AMP was obtained at 1.4 nM and maximal stimulation (3-fold basal level) at about 100 nM VIP. Chicken VIP and porcine secretin were agonists of porcine VIP but exhibited a 2-times higher and a 170-times lower potency, respectively. A high concentration (1·10⁻⁶ M) of glucagon, somatostatin, neurotensin, substance P, Met-enkephalin or Leu-enkephalin did not modify cAMP levels. The finding of a VIP-stimulated cAMP system in rat prostatic epithelial cells together with the previous characterization of high-affinity receptors for VIP in the same cell preparation, as well as the presence of VIP-containing neurones innervating the male genitourinary tract, strongly suggest that VIP may be involved in prostatic growth regulation and function.     

Stimulatory effect of hormonal signaling factors on (Ca2+−Mg2+)-ATPase activity in rat liver plasma membranes: Cross talk with regucalcin

The effect of hormonal signaling factors on (Ca²⁺–Mg²⁺)-ATPase activity in rat liver plasma membranes was investigated. The presence of inositol-glycan (10^–7–10^–5M), dibutyryl cAMP (10^–4 and 10^–3M) or inositol 1,4,5-trisphosphate (IP₃; 10^–6 and 10^–5 M) in the enzyme reaction mixture produced a significant increase in (Ca²⁺–Mg²⁺)-ATPase activity. These effects were completely inhibited by the presence of vanadate (10^–4 M), an inhibitor of the enzyme phosphorylation, and N-ethylmaleimide (5×10^–3 M), a SH group modifying reagent. Meanwhile, regucalcin, a Ca²⁺-binding protein isolated from rat liver cytosol, increased the enzyme activity by binding to the SH groups of (Ca²⁺–Mg²⁺)-ATPase in liver plasma membranes. The presence of regucalcin (0.25 M) with an effective concentration completely inhibited the effect of inositol-glycan (10^–5 M) to increase (Ca²⁺–Mg²⁺)-ATPase activity, while the effect of dibutyryl cAMP (10^–3M) or IP₃ (10^–5M) was not altered. The inositol-glycan effect was not modulated by the presence of dibutyryl cAMP or IP₃. Now, the preincubation of the plasma membranes with regucalcin did not modify the effect of inositol-glycan on the enzyme activity, suggesting that regucalcin competes with inositol-glycan for the binding to the plasma membranes. The present results suggest that there may be a cross talk with regucalcin and hormonal signaling factors in the regulation of (Ca²⁺–Mg²⁺)-ATPase activity in liver plasma membranes.     

Is there a “dopaminergic glial cell”?

Intracellular cAMP increased 9-fold in cerebral hemisphere primary cultures after incubation with dopamine (10^–4M). The effect was dose- and time-dependent (10^–6 M-10^–4M; 2–10 minutes). It was mimicked, to some extent, by the partial agonist apomorphine (10^–5 M-10^–4 M) and antagonized by fluphenazine (10^–5 M-10^–4 M). The elevation of cAMP caused by dopamine was incompletely antagonized by propanolol (10^–5 M-10^–4 M), obviating an interaction with -adrenergic receptors. A -adrenergic effect was antagonized by propranolol but only slightly by fluphenazine. The effect of dopamine on cAMP-level was more pronounced in a subpopulation of the hemisphere culture, i.e. in astroglial cultures from the striatum, 12-fold compared with controls at 10^–4 M. No dopamine stimulated formation of cAMP was found in primary cultures from brain-stem. The results demonstrated some heterogeneity among astroglial cells. The cultures used contained mainly astroglial-like cells, as judged from immnohistochemical localization mainly astroglial-like cells, as judged from immunohistochemical localization of the glial specific proteins S 100 and GFA (-albumin). No mature neurons or oligodendroglial cells have so far been demonstrated in the cultures.     

Regucalcin modulates hormonal effect on (Ca2+−Mg2+)-ATPase activity in rat liver plasma membranes

The interaction of various hormones and regucalcin on (Ca²⁺–Mg²⁺)-ATPase activity in rat liver plasma membranes was investigated. The presence of epinephrine (10^–6–10^–4 M), and insulin (10^–8–10^– M) in the reaction mixture produced a significant increase in (Ca²⁺–Mg²⁺)-ATPase activity, while the enzyme activity was decreased significantly by calcitonin, (3×10^–8–3×10^–6 M). These hormonal effects, except for calcitonin, were clearly inhibited by the presence of vanadate (10^–4 M) which can inhibit the Ca²⁺-dependent phosphorylation of enzyme. Meanwhile, regucalcin (0.25 and 0.50 M), isolated from rat liver cytosol, elevated significantly (Ca²⁺–Mg²⁺)-ATPase activity in the plasma membranes, although this elevation was not inhibited by vanadate (10^–4 M). the epinephrine (10^–5 M) or phenylephrine (10^–4 M)-induced increase in (Ca²⁺–Mg²⁺)-ATPase activity was disappeared in the presence of regucalcin; in this case the effect of regucalcin was also weakened. However, the inhibitory effect of calcitonin (3×10^–6 M) was not weakened by the presence of regucalcin (0.5 M). Moreover, GTP (10^–5 and 10^–4 M)-induced increase in (Ca²⁺–Mg²⁺)-ATPase activity was not seen in the presence of regucalcin (0.25 M). The present finding suggests that the activating mechanism of regucalcin on (Ca²⁺–Mg²⁺)-ATPase is not involved on GTP-binding protein which modulates the receptor-mediated hormonal effect in rat liver plasma membranes.     

D-Phe4]peptide histidine-isoleucinamide ([D-Phe4]PHI), a highly selective vasoactive-intestinal-peptide (VIP) agonist, discriminates VIP-preferring from secretin-preferring receptors in rat pancreatic membranes

The capacity of vasoactive intestinal peptide (VIP), peptide histidine-isoleucinamide (PHI), secretin, and a series of analogs to discriminate between VIP-preferring and secretin-preferring receptors that coexist in rat pancreatic plasma membranes was evaluated by their ability to inhibit [125I]iodo-VIP and [125I]iodo-secretin binding and to activate adenylate cyclase. VIP, the VIP analogs [D-His1]VIP, [D-Ser2]VIP, [D-Asp3]VIP and [D-Ala4]VIP, PHI, [D-Phe4]PHI, and secretin inhibited the binding of both ligands in a concentration range of 10(-11) M to 10(-5) M and with a selectivity factor varying from 18,000 to 0.1. The only exception was [D-Phe4]PHI that inhibited 125I-VIP binding only, with an IC50 of 7 nM, and with no inhibition of 125I-secretin binding at 10 microM. The peptides tested stimulated adenylate cyclase in the same membranes and the slope of the dose-effect curves indicated that all peptides, except [D-Phe4]PHI, interacted with at least two classes of receptors: VIP-preferring and secretin-preferring receptors. By contrast, the dose-effect curve of [D-Phe4]PHI activation of adenylate cyclase was monophasic and competitively modified by [D-Phe2]VIP (a VIP antagonist) but not by secretin(7-27) (a secretin antagonist), indicating an interaction with VIP-preferring receptors only. Thus, [D-Phe4]PHI appears to be a highly selective tool to characterize these receptors.     

β-Adrenoreceptors of multiple affinities in a clonal capillary endothelial cell line and its functional implication

-Adrenoreceptor has been studied in a clonal capillary endothelial cell line established from the vascular bed of the bovine adrenal medulla. [³H]Dihydroalprenolol ([³H]DHA) binding to the isolated plasma membranes from these cells has demonstrated the presence of -adrenoreceptors with two different affinities. the dissociation constants (K_d) have been found to be 0.27±0.09×10^–9 M and 2.96±0.31×10^–9 M, respectively with the corresponding B_max of 5.1±0.05 and 70.0±0.2 pmol/mg protein, respectively. Inhibition of [³H]DHA binding to the -receptor by atenolol (a ₁-antagonist) and ICI 118,551 (a ₁-antagonist) has suggested that the IC_50cor (=K_i) for atenolol and ICI 118,551 for high affinity site are 0.08±0.03×10^–12 M and 0.25±0.08×10^–12 M, respectively. This, therefore, indicates that both atenolol and ICI 118,551 are able to displace the bound ligand effectively but the ₁-selective antagonist atenolol is 3 times more potent than its ₂ counterpart, ICI 118,551. Displacement of [³H]DHA binding to the endothelial cell plasma membrane by the agonists isoproterenol, epinephrine and norephinephrine has established a relative order of K_i for these agents as isoproterenol (0.56±0.19×10^–9 M)–9 M)>-norepinephrine (0.71±0.24×10^–9 M) for the high affinity site. The corresponding values for the low affinity site, however, are 4.62±0.64×10^–9 M, 6.21±0.86×10^–9 M and 5.90±0.82×10^–9 M, respectively for the same agonists. Increased intracellular cAMP accompanied with cellular proliferation in the presence of isoproterenol has suggested not only the coupling of -adrenoreceptors to the adenylate cyclase system but also its involvement in endothelial cell proliferation.Abbreviations DHA Dihydroalprenolol - cAMP 3:5 cyclic adenosine monophosphate - DTT dithiothreitol - MEM minimal essential medium - 8Br-cAMP 8-bromo-adenosine 3:5 cyclic monophosphate     

Zinc compounds inhibit osteoclast-like cell formation at the earlier stage of rat marrow culture but not osteoclast function

The effect of zinc compounds on osteoclast-like cell formation in rat marrow culture in vitro was investigated. The bone marrow cells were cultured for 7 days in -minimal essential medium containing a well-known bone resorbing hormone (1, 25-dihydroxyvitamin D₃ and parathyroid hormone [1–34]). Osteoclast-like cell formation was estimated by staining for tartrateresistant acid phosphatase (TRACP), a marker enzyme of osteoclasts. The presence of 1, 25-dihydroxyvitamin D₃ (10^–8 M) or parathyroid hormone (PTH; 10^–8 M) induced a remarkable increase in osteoclast-like multinucleated cells (MNC). These increases were clearly inhibited by the presence of zinc sulfate or zinc-chelating dipeptide (-alanyl-L-histidinato zinc; AHZ) in the concentration range of 10^–7 to 10^–5 M. The inhibitory effect was seen at the earlier stage of osteoclast-like MNC formation. However, zinc compounds (10^–6 M) did not have an effect on PTH (10^–8 M)-induced osteoclast-like cell formation in the presence of EGTA (5 × 10^–4 M), dibucaine (10^–5 M) or staurosporine (10^–9 M). Moreover, when osteoclasts isolated from rat femoraldiaphyseal tissues were cultured for 24 h in the presence of zinc compounds (10^–7 to 10^–5 M), the compounds did not have an effect on cell numbers or lysosomal enzymes activity (acid phosphatase and -glucuronidase) in the cells. The present study clearly demonstrates that zinc compounds inhibit osteoclast-like cell formation at the earlier stage with differentiation of marrow cells.     

Exogeneous cyclic AMP blocks the muscarinic receptor-mediated intracellular Ca2+-release in the gastrulating chick embryo cells

Summary Exogeneous cyclic AMP (cAMP, 10^–8M), when added together with acetylcholine (ACh, 500 M) to dissociated chick embryo cells, blocked the ACh-stimulated increase in the level of cytosolic free Ca²⁺ ([Ca²⁺]_i). This inhibiting action of exogeneous cAMP is probably mediated by intracellular cyclic GMP (cGMP) and cAMP.     

Effects of epinephrine, glucagon and vasoactive intestinal polypeptide on chloride secretion by teleost opercular membrane

Summary The effects of epinephrine, glucagon and vasoactive intestinal polypeptide on chloride secretion by chloride cell-containing isolated opercular membranes from the seawater-adapted euryhaline teleost, the tilapiaSarotherodon mossambicus, have been examined. Epinephrine inhibits chloride secretion, measured as the short-circuit current (I _sc), via -receptors, in a dose-dependent fashion. The minimum effective dose is 10^–9 M, ED₅₀ equals 2×10^–7 M and maximal inhibition at 10^–5 M is nearly 80%. Inhibition of phosphodiesterase by isobutylmethylxanthine (IBMX; 10^–4 M), does not alterI _sc in untreated tissues, but it completely reverses the epinephrine inhibition ofI _sc, suggesting that hormones which modulate cAMP in chloride cells may alter chloride secretion. Glucagon and vasoactive intestinal polypeptide also stimulateI _sc in epinephrine-inhibited tissues, an effect potentiated by IBMX. The effect of glucagon is dose-dependent with a minimum effective dose of 10^–9 M, ED₅₀ equal to 8×10^–8 M and a maximum stimulation of 72% at 10^–5 M.Analysis of the effects of epinephrine and IBMX onI _sc and tissue conductance suggests that these agents act antagonistically on a nonconductive transport mechanism. It is proposed that IBMX and hormones which increase intracellular cAMP levels stimulate chloride secretion in epinephrine-inhibited tissues by stimulating a neutral sodium chloride cellular entry-step mechanism.Abbreviations ED ₅₀ effective dose causing half-maximal inhibition or stimulation - IBMX isobutylmethylxanthine - VIP vasoactive intestinal polypeptide     

On the Nature of the Three-Phase Response of Scenedesmus quadricauda Populations to the Action of Imazalil Sulfate

Three-phase dose responses of biological systems of different levels of organization are often called paradoxical because the biological effects are clearly manifested under low- and high-intensity treatments, but are absent during moderate-strength treatments. In this work, we found anomalous changes in the cell number of a green alga Scenedesmus quadricauda (Turp.) Breb. grown in the presence of the fungicide imazalil sulfate. At low imazalil concentrations (2.5 × 10^–9–2.5 × 10^–6 M), the slow increase in the cell number as compared to an untreated culture was not related to cell death. As seen by the dynamics of the population structure and cell functional characteristics (photosynthesis, thermal stability of photosynthetic membranes, etc.), the decrease in the growth rate at low concentrations of imazalil (2–10 × 10^–9 M) was due to a long-term arrest of cell division in a fraction of the cell population rather than to a decrease in the rate of division. The absence of a toxic effect or even a slight stimulation of culture growth at moderate concentrations (0.05–1.25 × 10^–6 M) was due to the resumption of cell division after a temporal cessation. At these concentrations, imazalil induced cell stress and adaptive elevation of cell tolerance to the fungicide (acclimation). Cell death was observed only at a high fungicide content in the medium (6.25 × 10^–6 and higher). Thus, the three-phase (bimodal) dose response corresponds to two regimes (steady-states) of cell functioning which differ in cell sensitivity to external stimuli. The low-sensitivity state, which is characteristic of cells that have experienced stress, is likely to be the state known as hormesis.     

Effect of PT-treatment on ANP-mediated inhibition of adenylate cyclase and amylase release in rat parotid gland

Effects of pertussis toxin (PT) treatment on atrial natriuretic peptide (ANP)-mediated inhibition of adenylate cyclase and amylase release were investigated in rat parotid gland. Adenylate cyclase activity stimulated by GTPS in PT-treated membranes was much larger than that in normal membranes. ANP dose-dependently inhibited adenylate cyclase stimulated by GTPS in control rat parotid membranes, however in membranes prepared from PT-injected (in vivo) rat parotid gland, ANP did not inhibit adenylate cyclase. ANP(10^–7M) inhibited cAMP accumulation stimulated by forskolin (10^–6M) in control rat parotid acinar cells by about 34%, however, in PT-treated cells, the inhibitory effect of ANP was attenuated completely. In control cells, amylase release stimulated by isoproterenol (10^–6M) and forskolin (10^–6M) were also depressed by ANP (10^–7M) by 27 and 30%, respectively. The inhibitory response of ANP on amylase release was completely attenuated by PT-treatment. Gi was detected as a ADP-ribosylated 41-KDa protein by incubation of parotid membranes with PT and [-³²P]NAD. In rat parotid gland, these results suggested that ANP mediates adenylate cyclase/cAMP system and consequently reduces amylase release through ANP-C receptor coupled to Gi. (Mol Cell Biochem)139: 53–58, 1994)     

Growth and uptake kinetics of a facultatively oligotrophic bacterium at low nutrient concentrations

In oligotrophic waters, not only community structure but also physiological properties of heterotrophic bacteria are influenced by the concentration of organic matter.The relationship between growth rate of two facultatively oligotrophic strains ofAeromonas sp. No. 6 andFlavobacterium sp. M1 was studied in comparison with that of two eutrophic strains ofEscherichia coli 7020 andFlavobacterium sp. M2. These strains had two or three different substrate constants (Ks values) depending on substrate concentrations: Ks values for the two former were remarkably lower than those for the two latter. For instance, Ks value forAeromonas sp. No. 6 was about 8.9M when substrate concentration was greater than 53M and about 1.1M when substrate concentration was less man 53M. InE. coli the Ks value was about 260M at greater than 5600M and about 47M at less than 5600M substrate concentration.Uptake kinetics ofAeromonas sp. grown in a medium containing 2.7 mM glutamate (H-cell) and 0.11M glutamate (L-cell) have been determined for the intact cells. H-cell had two distinct values of Km for glutamate assimilation and respiration, and L-cell had three distinct values of Km for glutamate assimilation and respiration: In H-cell Km of assimilation was 2.8×10^–7 M and 1.5×10^–4 M, and Km of respiration was 2.3×10^–7 M and 1.7×10^–4 M; in L-cell Km of assimilation was 7.4×10^–8 M, 8.3×10^–6 M, and 1.3×10^–4 M, and Km of respiration was 2.5×10^–7, 8.9×10^–6M, and 1.7×10^–4 M. More than 60% of glutamate taken up by the H- and L-cells was respired when the substrate concentration was less than 10^–6 M, although at greater than 10^–6 M, 50% and 30% of glutamate was respired by H-cells and L-cells, respectively. These results suggest that the facultatively oligotrophic bacteria grow with high efficiency in environments with extremely low nutrient concentration, such as oligotrophic waters of lakes and ocean, as compared with in their growth in conditions of high nutrient concentraton, such as nutrient broth.     

Stimulatory effect of β-alanyl-L-histidinato zinc on cell proliferation is dependent on protein synthesis in osteoblastic MC3T3-E1 cells

The effect of -alanyl-L-histidinato zinc (AHZ) on bone metabolism was investigated in osteoblastic MC3T3-El cells. Cells were cultured for 3 days at 37°C in a CO₂ incubator in plastic dishes containing -modified minimum essential medium supplemented with 10% fetal bovine serum. After the cultures, the medium was exchanged for that containing 0.1% bovine serum albumin plus various concentrations of AHZ or other reagents, and the cells were cultured further for appropriate periods of time. The presence of AHZ (10^–7–10^–5M) stimulated the proliferation of cells. AHZ (10^–6 and 10^–5M) increased deoxyribonucleic acid (DNA) content in the cells with 48hr-culture. This increase was completely blocked by the presence of cycloheximide (10^–6M) or hydroxyurea (10^–3M). Also, the presence of cycloheximide (10^–6M) completely inhibited the AHZ (10^–5M)-induced increase in the proliferation of cells. Meanwhile, parathyroid hormone (10^–7M), estrogen (10^–9M) and insulin (10^–M) significantly increased cellular DNA content. However, these hormonal effects clearly lowered in comparison with that of AHZ (10^–5M). Dibutyryl cyclic AMP (10^–4M) and zinc sulfate (10^–5M) did not cause a significant increase in cellular DNA content. The present results support the view that AHZ has a direct specific proliferative effect on osteoblastic cellsin vitro and that this effect is dependent on protein synthesis.     

In vitro propagation of the bamboo (Bambusa tulda Roxb.) through shoot proliferation

An efficient protocol has been developed for the in vitro propagation of Bambusa tulda through shoot proliferation. Shoots from 3-week-old aseptically grown seedlings were used to initiate cultures. Multiple shoots were obtained on liquid Murashige and Skoog (MS) medium supplemented with 6-benzylaminopurine (8×10^–6M) and kinetin (4×10^–6M). Continuous shoot proliferation at a rate of 4–5 fold every three weeks was achieved through forced axillary branching. More than 90% of the shoots could be rooted on a modified MS medium containing indoleacetic acid (1×10^–5M) and coumarin (6.8×10^–5M). Following simple hardening procedures, the in vitro raised plants were transferred to the soil with more than 80% success.Abbreviations BAP 6-benzylaminopurine - 2-ip 6-,-dimethylallylaminopurine - Kn kinetin - IAA 3-indoleacetic acid - IBA 3-indolebutyric acid - NAA 1-naphthaleneacetic acid     

Functional and specific vasoactive intestinal peptide receptors in enterocytes isolated from fetal or adult rats

Functional and specific VIP receptors (relative potencies: VIP greater than PHI greater than secretin) have been characterized (cAMP generation) in enterocytes isolated from rat fetuses at 19 days gestation, after incubation at 37 degrees C in the presence of IBMX. In fetuses, VIP is about 6 times more potent (EC50 = 2.5 X 10(-10) M) than in adults (EC50 = 15 X 10(-10) M). This difference is not observed for PGE2, and is not related to cAMP-PDE activities (Km, Vmax). It is suggested that VIP may regulate the differentiation and function of enterocytes during the fetal life in rats.     

Inhibition of abscisic acid biosynthesis inCercospora rosicola by triarimol

The fungicide triarimol was tested for its effect on abscisic acid (ABA) accumulation in growing culturesof Cercospora rosicola. ABA accumulation was reduced by approximately 50% with 10^–8 M triarimol. Growth ofC. rosicola, as measured by dry weight accumulation, was inhibited by triarimol concentrations at or greater than 10^–7 M. These results are compared with those obtained with clomazone, ancymidol, and paclobutrazol, which inhibit ABA accumulation by 50% at concentrations of 5 × 10^–5, 5 × 10^–6, and 5 × 10^–7 M, respectively. Triarimol, therefore, is among the most potent inhibitors of ABA biosynthesis reported to date. Feeding studies with [¹⁴C]mevalonic acid confirmed the inhibition of ABA biosynthesis by 5 × 10^–8 M triarimol. These results support previous suggestions that one or more of the steps in the ABA biosynthetic pathway from mevalonic acid is catalyzed by cytochrome P-450. Feeding studies with 1-deoxy-[²H]-ABA in resuspended cultures ofC. rosicola show that the conversion of this substrate is not inhibited by triarimol.     

Effect of Glycine and Strychnine on Cl–-Activated Mg2+-ATPase from Bream Brain Microsomes (Abramis bramaL.)

The effect of glycine and strychnine on Mg²⁺-ATPase from the microsomal fraction of the bream (Abramis bramaL.) brain was studied. The glycine in the concentration range 10^–7–10^–4M activates the enzyme. The effect of glycine on Mg²⁺-ATPase is obviated by 100 M strychnine. The strychnine in the concentration range 5–90 M activates the basal Mg²⁺-ATPase but decreases the effect of the enzyme activation by 10^–4M glycine. The effect of Cl^–on Mg²⁺-ATPase depends on the substrate concentration (Mg²⁺-ATP) and is not observed in the presence of 100 M strychnine. A receptor-dependent pathway of glycine and strychnine action on Cl^–-activated Mg²⁺-ATPase from bream brain microsomes is proposed.     

Effects of Zn2+ and Cu2+ on growth,lignin degradation and ligninolytic enzymes in Phanerochaete chrysosporium

The influence of Zn²⁺ (6.0 × 10^–3 –18.0 × 10^–3 M) and Cu²⁺ (4 × 10^–4 –1.2 × 10^–4 M) in the basal medium on mycelial growth (dry weight), activities of lignin peroxidase (Lip), manganese peroxidase (Mnp), solubilization, and mineralization (¹⁴CO₂ evolution) of lignin during a period of 3 weeks was studied in Phanerochaete chrysosporium strain MTCC-787. Highest mycelial growth was obtained at 0.6 M Zn²⁺ and 0.4 M Cu²⁺ levels. Enzyme activities were found to increase up to the highest levels of both the trace elements. However, Zn²⁺ had a relatively more stimulatory effect on Lip production and the reverse was true in case of Cu²⁺. [¹⁴C]Lignin solubilization was also promoted by higher levels of both trace elements. Mineralization of [¹⁴C]lignin was optimal at 6.0 M Zn²⁺ and 1.2 M Cu²⁺. The stimulatory effect of Zn²⁺ on Lip production was correlated with higher rates of [¹⁴C]lignin mineralization.