Studies on polyol metabolism in Aspergillus niger

Summary Sorbitol dehydrogenase has been purified about 26 fold from a strain of Aspergillus niger, growing on sorbitol as the sole source of carbon. An absolute specificity of this enzyme for sorbitol, fructose, NAD and NADH was observed. The K _m for sorbitol and fructose were found to be 9.8x10^-5 M and 6.6x10^-4 M respectively. The enzyme was inhibited by pCMB, NaF and other metal ions studied. The enzyme was slightly activated by Fe⁺⁺⁺.Part of this work was presented at the All India Conference of Microbiologists held at Baroda, 1968/69.     

Purification and characterization of L-mimosine synthase from Leucaena leucocephala

L-Mimosine synthase has been isolated from Leucaena leucocephala seedlings and purified 280-fold by heat treatment, ammonium sulphate fractionation, gel filtration and ion-exchange chromatography. The enzyme was shown to be homogeneous by gel electrophoresis (MW 64 000±2000) and to consist of two identical subunits with MWs of 32 000±2000. The purified enzyme has a K_m value of 6.25 x 10^?3 M for O-acetyl-L-serine and 5.0 x 10^?3 M for 3,4-dihydroxypyridine. In these and other properties, the enzyme differs from β-(pyrazol-1-yl)-L-alanine synthase from Citrullus vulgaris seedlings.     

Hexosediphosphatase from spinach chloroplasts: Purification,crystallization and some properties

Hexosediphosphatase (d-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) has been isolated, purified, and crystallized, from previously isolated spinach chloroplasts. The effects of various anions, cations, and sulfhydryl compounds were tested, and activation by Mg²⁺, glycine, HCO₃^?, and sulfhydryl compounds is described. The purified enzyme is very specific for fructose 1,6-diphosphate and does not attack sedoheptulose-1,7-bisphosphate. The s₂₀ value of the enzyme was 7.7, from which the molecular weight of the enzyme was estimated as 140 000.     

Activation of solubilized liver membrane adenylate cyclase by nucleotides

Liver plasma membranes isolated from hypophysectomized rats were treated with 0.1 M Lubrol-PX, a nonionic detergent, and centrifuged at 165,000 × g for 1 hour. Adenylate cyclase activity remaining in the supernate had a specific activity that was at least equal to that of the particulate enzyme. The activity of the solubilized, non-sedimentable adenylate cyclase, as well as the membrane bound enzyme, was increased by GTP, ITP, and GMP-PCP at 10^?4 M. The activity of the solubilized, non-sedimentable enzyme increased linearly with GTP from 10^?6 to 10^?4 M but there was no further increase in the activity of the solubilized enzyme with 10^?3 M GTP. In contrast, the particulate liver membrane enzyme activity increased exponentially with GTP from 10^?6 to 10^?4 M and was further increased by 10^?3 M GTP. These data indicate that GTP, ITP or GMP-PCP have direct effects on solubilized adenylate cyclase. This effect is in addition to a role of nucleotides in modifying membrane structure (16).     

Purification and properties of UDP-glucose: coniferyl alcohol glucosyltransferase from suspension culturesof Paul's scarlet rose.

UDP-glucose:coniferyl alcohol glucosyltransferase was isolated from 10-day-old, darkgrown cell suspension cultures of Paul's scarlet rose. The enzyme was purified 120-fold by (NH₄)₂SO₄ fractionation and chromatography on DEAE-cellulose, hydroxyapatite, and Sephadex G-100. The enzyme has a pH optimum of 7.5 in Tris-HCl buffer, required an -SH group for activity, and is inhibited by ?-chloromercuribenzoate and EDTA. Its molecular weight is estimated to be 52,000. The enzyme is specific for the glucosylation of coniferyl alcohol (K_m 3.3 × 10^?6 M) and sinapyl alcohol (K_m 5.6 × 10^?6 M). With coniferyl alcohol as substrate the apparent K_m value for UDP-glucose is 2 × 10^?6m. The enzyme activity can be detected in a number of callus-tissue and cell-suspension cultures. The role of this enzyme is believed to be to catalyze the transfer of glucose from UDPG to coniferyl (or sinapyl) alcohol as storage intermediates in lignin biosynthesis.     

Agmatine deiminase in rice seedlings

Agmatine deiminase activity in rice embryos increased gradually upto 24 hr during germination and then decreased. Gibberellic acid and kinetin inhibited the activity when added to the germination medium. The enzyme was purified 717 fold with specific activity 788.5 nkat/mg protein and yield 8.8%. The M_r of the native enzyme was 18.3 x 10⁴ and the enzyme was a dimer of two identical subunits. The pH and temperature optimum of the enzyme were 6.0 and 28° respectively. The enzyme followed typical Michaelis-Menten kinetics with a K_m value of 1.5 x 10^?2 M. The enzyme activity was inhibited by various divalent cations and spermidine and spermine, but putrescine showed no effect.     

Cerebral microvessels contain a beta 2-adrenergic receptor

Cerebral microvessels isolated from cat forebrain contain a specific β-adrenergic-sensitive adenylate cyclase. Among various compounds tested, the most potent activator of enzyme activity is isoproterenol (k_a = 1.4 × 10^?7M), followed in order by epinephrine (k_a= 1.5 × 10^?6M), norepinephrine (k_a= 1.4 × 10^?5M) and phenylephrine (k_a> 3 × 10^?4M). Isoproterenol-stimulated enzyme activity is blocked by propranolol (k_i= 2.4 × 10^?9M, IPS 339 (k_i= 4 × 10^?9M), H35/25 (k_i = 1.2 × 10^?7M), atenolol (k_i= 5.9 × 10^?6M) and practolol (k_i= 1.8 × 10^?5M). These agonist and antagonist properties are quite similar to those demonstrated by β₂-adrenergic receptors and β₂-stimulated adenylate cyclase present in other tissues and indicate that the majority of adenylate cyclase-associated adrenergic receptors in cerebral microvessels are β₂. The findings are relevant to physiological studies of cerebral blood flow and vascular permeability.     

The Effect of Hydrogen Peroxide on the Growth of Microscopic Mycelial Fungi Isolated from Habitats with Different Levels of Radioactive Contamination

The effect of hydrogen peroxide (10^?9–10^?1 M) on the mycelial growth of the fungi Alternaria alternata, Cladosporium cladosporioides, Mucor hiemalis, and Paecilomyces lilacinus has been studied. The growth of fungi isolated from habitats with a background level of radioactive contamination was stopped by H₂O₂ concentrations equal to 10^?3 and 10^?2 M, whereas the growth of fungi that were isolated from habitats with high levels of radioactive contamination was only arrested by 10^?1 M H₂O₂. The response of the different fungi to hydrogen peroxide was of three types: (1) a constant growth rate of fungal hyphae at H₂O₂ concentrations between 10^?9 and 10^?4 M and a decrease in this rate at 10^?3 M H₂O₂, (2) a gradual decrease in the growth rate as the H₂O₂ concentration was increased, and (3) an increase in the growth rate as the H₂O₂ concentration was increased from 10^?6 to 10^?5 M. The melanin-containing species A. alternata and C. cladosporioides exhibited all three types of growth response to hydrogen peroxide, whereas the light-pigmented species M. hiemalis and P. lilacinus showed only the first type of growth response. A concentration of hydrogen peroxide equal to 10^?1 M was found to be lethal to all of the fungi studied. The most resistant to hydrogen peroxide was found to be the strain A. alternata 56, isolated from the exclusion zone of the Chernobyl Nuclear Power Plant.     

Inhibition by indomethacin and aspirin of 15-hydroxy-prostaglandin dehydrogenase in vitro

15-Hydroxyprostaglandin dehydrogenase from bovine lung was purified 7.4 times to a specific activity of 1.4 mU/mg of protein. The isoelectric point was estimated to 5.4 and the molecular weight by gelfiltration to 40,000. K_m for prostaglandin E₁ and for NAD⁺ were found to be 3.4 μM and 1.1 × 10^?4M respectively. The enzyme was inhibited by indomethacin and aspirin. The indomethacin inhibition was found to be non-competitive to prostaglandin E₁ having a K_i=1.4 × 10^?4M and a K_i^′=1.6 × 10^?5M.     

Purification and properties of fructose diphosphate aldolase from Ascaris suum muscle

A fructose diphosphate aldolase has been isolated from ascarid muscle and crystallized by simple column chromatography and an ammonium sulfate fractionation procedure. It was found to be homogeneous on electrophoresis and Sephadex G-200 gel filtration. This enzyme has a fructose diphosphate/fructose 1-phosphate activity ratio close to 40 and specific activity for fructose diphosphate cleavage close to 11. K_m values of ascarid aldolase are 1 × 10⁻⁶m and 2 × 10⁻³m for fructose diphosphate and fructose 1-phosphate, respectively. The enzyme reveals a number of catalytic and molecular properties similar to those found for class I fructose diphosphate aldolases. It has C-terminal functional tyrosine residues, a molecular weight of 155,000, and is inactivated by NaBH₄ in presence of substrate. Data show the presence of two types of subunits in ascarid aldolase; the subunits have different electrophoretic mobilities but similar molecular weights of 40,000. Immunological studies indicate that the antibody-binding sites of the molecules of the rabbit muscle aldolase A or rabbit liver aldolase B are structurally different from those of ascarid aldolase. Hybridization studies show the formation of one middle hybrid form from a binary mixture of the subunits of ascarid and rabbit muscle aldolases. Hybridization between rabbit liver aldolase and ascarid aldolase was not observed. The results indicate that ascarid aldolase is structurally more related to the mammalian aldolase A than to the aldolase B.     

Purification and properties of a D-fructose 1,6-bisphosphatase from Saccharomyces cerevisiae.

Fructose 1,6-bisphosphatase (EC 3.1.3.11) from Saccharomyces cerevisiae has been purified to homogeneity. A molecular weight of 115,000 has been obtained by gel filtration. The enzyme appears to be a dimer with identical subunits. The apparent K_m for fructose bisphosphatase varies with the Mg²⁺ concentration of the enzyme, being 1 × 10^?6m at 10 mm Mg²⁺ and 1 × 10^?5m at 2 mm Mg²⁺. Other phosphorylated compounds are not significantly hydrolyzed by the enzyme. An optimum pH of 8.0 is exhibited by the enzyme. This optimum is not changed by addition of EDTA. AMP inhibits the enzyme with a K_i of 8.0 × 10^?5m at 25 °C. The inhibition is temperature dependent, the value of K_i increasing with raising temperature. 2-Deoxy-AMP is also inhibitory with a K_i value at 25 °C of 1.6 × 10^?4m. An ordered uni-bi mechanism has been deduced for the reaction with phosphate leaving the enzyme as the first product and the fructose 6-phosphate as the second one.     

The isolation of pig liver monoamine oxidase

Monoamine oxidase from pig liver has been isolated and purified approximately three hundred-fold. This enzyme has a molecular weight of 1,200,000, is highly polymeric, and contains subunits of molecular weight 146,000, as determined by Sephadex chromatography. The apparent K_m at 25°C is 1.28 × 10^?6 M at pH 9.0 (0.05 M glycine) and 1.74 × 10^?5 M at pH 7.2 (0.2 M phosphate) using benzylamine as a substrate. This enzyme contains approximately 8 copper(II) ions per 1,200,000 molecular weight.     

Stimulation of yeast phosphofructokinase activity by Fructose 2,6-bisphosphate

Fructose 2,6-bisphosphate is a powerful activator of yeast phosphofructokinase when assayed at pH levels of ≥7.0. Half maximal stimulation of enzyme activity occurs at 10^?7 M levels of Fru 2,6-P₂ concentration. This stimulating effect by Fru 2,6-P₂ can be synergistic to that exerted by AMP in counteracting the inhibition of phosphofructokinase activity by ATP. The affinity (S_0.5) of the yeast enzyme to fructose 6-phosphate changes from 1.5 mM in the absence of Fru 2,6-P₂ to 40 μM in its presence.     

Electron transport systems of Candida utilis. Purification and properties of the respiratory chain-linked external NADH dehydrogenase+

The respiratory chain-linked external NADH dehydrogenase has been isolated from Candida utilis in highly purified form. The enzyme is soluble and has a molecular weight of approx. 1.5 · 10⁶. The enzyme contains two moles of FMN per mole of enzyme and is composed of two large subunits of mol. wt. 270 000 and eight smaller subunits of mol. wt. 135 000. Iron and copper are present in the preparations, but appear to be contaminants. The enzyme catalyzes the oxidation of NADH and NADPH at nearly equal rates and reacts readily with 2,6-dichlorophenolindophenol, CoQ₆ and CoQ₁ derivatives as acceptors. Rotenone (10^?5 M) and seconal (10^?3 M) do not inhibit enzymatic activity.     

Studies on fructosyl transferase from Agave americana

The possible role of fructosyl transferase in the biosynthesis of fructosans in Agave americana was investigated. This enzyme was extracted from A. americana stem and purified 17.5-fold by salt fractionation and DEAE-cellulose chromatography. The optimum conditions for the enzyme were pH 6. 1, temperature 37°, substrate concentration 20% and K_m 3.6 × 10^?1 M; Ag⁺, Pb ²⁺, Hg²⁺, Al³⁺, Sn²⁺, CN^? acted as inhibitors and Ca²⁺, Mg²⁺, Co²⁺ and Li⁺ actemd as activators. Only sugars of the type F ～ R (R-aidose), e.g. sucrose and raffinose acted as substrates for the enzyme. The donor acceptor specificity of the enzyme was studied extensively. Sugars sucrose. None of the intermediates of fructosan biosynthesis from sucrpse acted as fructose donors. The possible acceptors from sucrose and raffinose. The enzyme was capable of building up oligosaccharides up to FIOG from sucrose. None of the intermediates of fructosan biosynthesis from sucrose acted as fructose donors. The possible mechanism of fructosan biosynthesis from sucrose is discussed.     

TYROSINE HYDROXYLASE IN BOVINE CAUDATE NUCLEUS

Approximately 80 per cent of tyrosine hydroxylase activity in bovine caudate nucleus was particle-bound. The rest of the activity was found in the soluble fraction. The enzyme activity in crude tissue preparations was inhibited, probably by the presence of endogenous inhibitors. Dilution of crude tissue preparations such as the crude mitochondrial fraction caused an increase in the specific activity. The particle-bound enzyme was solubilized by incubation with trypsin. The presence of deoxycholate increased the degree of solubilization. The activity of the solubilized enzyme from the washed particles was also inhibited, but the subsequent purification by ammonium sulphate could eliminate the inhibition. The solubilized enzyme was partially purified by ammonium sulphate fractionation and Sephadex G-150 chromatography. A tetrahydropteridine and ferrous ion were required as cofactors for the partially purified enzyme. Among various divalent cations, only ferrous ion could activate the partially purified enzyme. The enzyme was inhibited by L-α-methyl-p-tyrosine and catecholamines such as dopamine. The optimum pH was found between 5.5 and 6.0. K_m values toward tyrosine, 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine and Fe²⁺, were approximately 5 × 10^?5 M, 1 × 10^?4 M and 4 × 10^?4 M, respectively.     

Role of casein on induction and enhancement of production of a bacterial milk clotting protease from an indigenously isolated Bacillus subtilis

Aims: To isolate and enhance the yield of a bacterial milk clotting protease (MCP) through process optimization and scale up. Materials and Results: Bacillus subtilis was isolated as MCP producer with good milk clotting activity (MCA) per proteolytic activity (PA) index. The enzyme production was inducible with casein and enhanced with fructose and ammonium nitrate resulting in 571·43 U ml^?1 of enzyme. Conclusions: Medium containing 4% fructose, 0·75% casein, 0·3% NH₄NO₃ and 10 mmol l^–1 CaCl₂, pH 6·0, inoculated with 4% (v/v) inoculum, incubated at 37°C, 200 rev min^?1 for 72 h gave maximum production. A 6·67‐fold increase in MCP yield with very high MCA per PA index was observed after final optimization indicating similarity to rennets. Significance and Impact of the Study: Mostly fungal MCPs have been reported. The MCA and MCA per PA index of this bacterium is comparable to that of many fungal reports and better than quite a few bacterial MCPs. Thus, this enzyme by B. subtilis has good probability of successful use in cheese production.     

Stimulatory effect of prostaglandin E1 on thyroliberin-induced α-melanotropin release from perifused neuro-intermediate lobes of frog pituitary gland

A possible direct effect of prostaglandins on α-melanotropin (α-MSH) release at the level of the intermediate lobe of the frog pituitary was investigated $\text{in vitro}$ using a perifusion system technique. The effect of prostaglandins was studied on both spontaneous and TRH-stimulated α-MSH secretion. No significant effect of PGE₁, PGE₂, PGF_1α or PGF_2α on basal release of α-MSH could be detected. Indomethacin did not alter the α-MSH release induced by TRH. Conversely a significant increase in TRH-induced α-MSH secretion was observed in the presence of 1 x 10^?6M PGE₁. This magnifying effect was directly related to the concentration of TRH for doses ranging from 1 x 10^?8M to 1 x 10^?6M.     

Somatostatin binding to pituitary plasma membranes.

A method has been developed for the study of somatostatin binding to anterior pituitary plasma membranes. When 5×10^?9M [¹²⁵I]Tyr¹-somatostatin (SA 18 Ci/mmol) was incubated with isolated pituitary plasma membranes (protein = 100 μg), 13.6% of total radioactivity was bound excluding nonspecific binding. The Scatchard plot could be resolved into two distinct components and analyzed to yield: K₁diss = 3.3×10^?8M and K₂diss = 7.7×10^?6M. This binding was shown to be specific for somatostatin.     

Tricyclohexyltin hydroxide effects on cationic and substrate activation kinetics of beta-adrenergic–stimulated cardiac Ca2+-ATPase

Previous studies from this laboratory have indicated that tricyclohexyltin hydroxide (Plictran) is a potent inhibitor of both basal- and isoproterenol-stimulated cardiac sarcoplasmic reticulum (SR) Ca²⁺-ATPase, with an estimated IC-50 of 2.5 × 10^?8M. The present studies were initiated to evaluate the mechanism of inhibition of Ca²⁺-ATPase by Plictran. Data on substrate and cationic activation kinetics of Ca²⁺-ATPase indicated alteration of V_max and K_m by Plictran (1 and 5×10^?8M), suggesting a mixed type of inhibition. The beta-adrenergic agonist isoproterenol increased V_max of both ATP- and Ca²⁺-dependent enzyme activities. However, the K_m of enzyme was decreased only for Ca²⁺ Plictran inhibited isoproterenol-stimulated Ca²⁺-ATPase activity by altering both and V_max and K_m of ATP as well as Ca²⁺-dependent enzyme activities, suggesting that after binding to a single independent site, Plictran inhibits enzyme catalysis by decreasing the affinity of enzyme for ATP as well as for Ca²⁺ Preincubation of enzyme with 15 μM cAMP or the addition of 2mM ATP to the reaction mixture resulted in slight activation of Plictran-inhibited enzyme. Pretreatment of SR with 5 × 10^?7M propranolol and 5 × 10^?8M Plictran resulted in inhibition of basal activity in addition to the loss of stimulated activity. Preincubation of heart SR preparation with 5 × 10^?5M coenzyme A in combination with 5 × 10^?8M Plictran partly restored the beta-adrenergic stimulation. These results suggest that some critical sites common to both basal- and beta-adrenergic-stimulated Ca²⁺-ATPase are sensitive to binding by Plictran, and the resultant conformational change may lead to inhibition of beta-adrenergic stimulation.