Biochimica et Biophysica Acta (BBA) - Enzymology and Biological Oxidation最新文献

In Escherichia coli K₁₂,

• 1.

  1. A single mutation can lead to the concomitant modification or to the concomitant loss of the two activities, threonine-sensitive β-aspartokinase (ATP: L-aspartate 4-phosphotransferase, EC 2.7.2.4) and threonine-sensitive homoserine dehydrogenase (L-homoserine: NADP⁺ oxidoreductase, EC 1.1.1.3).

• 2.

  2. The two activities cannot be separated and the ratio of the specific activities remains constant throughout a 600-fold purification.

• 3.

  3. The substrates of one of the activities are inhibitors of the otther activity. The observed inhibitions are specific.

• 4.

  4. The threonine-sensitive aspartokinase is protected against thermal inactivation by NADPH, a substrate of the homoserine dehydrogenase.

• 5.

  5. The conclusion is drawn that the two activities under study are carried by a single protein molecule. The apparent molecular mass of this complex protein is changed in some mutants. There is no apparent correlation between the apparent molecular mass and the cooperativity of inhibitor molecules.

• 6.

  6. The significance of these findings is discussed in terms of metabolic regulation and intracellular topology.

Mitochondria of scutella of a maize inbred were allowed to respire in the presence of indoleacetic acid. Greatest enhancement of , P/N and P/O was observed with indoleacetic acid concentration around 1.07 · 10⁻¹⁰ M. At concentrations above 1.07 · 10⁻⁸ M, O₂ uptake was greatly inhibited while phosphorylation was inhibited to a lesser degree. It was shown that enhancement of mitochondrial activity is dependent on CoA; without added CoA, effects of indoleacetic acid were slight. The most effective concentration of CoA was shown to be 0.1 mg/2.8 ml reaction mixture. In the presence of 1.07 · 10⁻¹⁰ M indoleacetic acid, rate of O₂ uptake measured at 3-min intervals was greatly increased. In addition, with indoleacetic acid in the reaction mixture, mitochondria showed an almost immediate enhancement of activity while the control reaction and the reaction with high concentration of indoleacetic acid (1.07 · 10⁻⁵ M) exhibited a lag of 3–4 min. With regard to the relationship of CoA and indoleacetic acid-induced stimulation of rate of mitochondrial O₂ uptake, two points were observed: without added CoA, the rate of O₂ uptake is sharply reduced and there is a lag of 7 min before mitochondria show any O₂ uptake.

The results suggest that indoleacetic acid enhances mitochondrial activity by affecting the enzyme(s) of the oxidative phosphorylation pathway. It is suggested that indoleacetic acid accomplishes such enhancement by acting as an allosteric effector.

• 1.

  1. A relatively simple and reproducible method for the isolation and purification of viral neuraminidases, as already reported in a preliminary note, has been shown to be of general usefulness for influenza virus enzymes but to a lesser extent for parainfluenza virus enzymes. The properties of the viral enzymes prepared in this way are presented.

• 2.

  2. A comparative investigation of the properties of the enzymes of A2 virus, fowl plague virus (FPV), and Newcastle disease virus (NDV) revealed many differences among them. This was particularly evident in their antigens; minor differences were found in the pH optima, $\text{K}{}_{\mathrm{m}}$, substrate specificity and heat stability of the enzymes from the 3 representative myxoviruses. FPV and NDV enzymes have not been previously characterized.

• 3.

  3. The sedimentation coefficients of these enzymes were in the same range as Those measured by the transport and optical methods (9–10 S). This is in agreement with the values of other influenza enzymes prepared and analyzed by other techniques (9–10 S), but contrasts with the value of 5.5 S for a bacterial neuraminidase, Vibrio cholerae enzyme.

• 4.

  4. The final purity of the A2 virus and FPV enzymes was determined by preparing antisera to the enzymes. Such antisera were found to be devoid of antibodies against other virus-specific surface antigen(s). The utility of highly specific antiserum for investigating the role of neuraminidase during virus multiplication, and the use of the antigenic type-specific property of viral enzymes as a genetic marker are discussed.

• 1.

  1. The tryptic hydrolysis of cytochrome b₂ (yeast l-lactate: cytochrome c oxidoreductase, EC 1.1.2.3) liberates a cytochromic polypeptide which can be separated from the other fragments by gel filtration.

• 2.

  2. The properties of this new product, called “noyau cytochromique b₂”, have been investigated: the molecular weight is about 11 000 and this molecule is associated with one heme group; its spectral properties are very similar in the visible region to those of cytochrome b₂. The redox potential is −0.028 V to be compared with the value 0.000 V relative to cytochrome b₂ (pH 7.00; 30°). Severa, different components have been detected by electrophoresis. These data have been used in a discussion on the structural aspects of the active molecule of lactate dehydrogenase.

• 1.

  1. Cytochrome $\text{c}{}_{552}$ and hydrogenase (EC 1.12.1.1) activities have been compared in Escherichia coli and Escherichia aurescens cells grown aerobically and anaerobically in both complex and defined media.

• 2.

  2. Sodium formate added to the growth media stimulates synthesis of increased amounts of cytochrome $\text{c}{}_{552}$.

• 3.

  3. Extensive washing in 0.1 M phosphate buffer (pH 7.4), extensive sonication, and washing with 0.2% w/v sodium deoxycholate all solubilise cytochrome $\text{c}$ from hydrogenase-active membranes.

• 4.

  4. Residues from the above procedures still show hydrogenase activity.

• 5.

  5. Cells grown anaerobically with nitrate s terminal electron acceptor contain greatly enhanced amounts of cytochrome: these cells do not have hydrogenase, hydrogenlyase or soluble viologen-linked formic dehydrogenase activities.

The relationship of cytochrome $\text{c}{}_{552}$ to hydrogenase is discussed.

Extramitochondrial glycerophosphate dehydrogenase (L-glycerol-3-phosphate: DPN⁺ oxidoreductase, EC 1.1.1.8) was purified and crystallized from honeybee (Apis mellifera) thoraces. The isolation procedure is quite simple, since it consists merely of a series of (NH₄)₂SO₄ precipitations.

The crystalline enzyme is homogeneous according to the following criteria: recrystallization to constant specific activity, electrophoresis on cellulose acetate strips, absence of 3 other glycolytic enzyme activities, chromatography on Sephadex G-200, and immunodiffusion on cellulose acetate strips.

Sedimentation velocity studies indicate that the native protein readily associates at moderate protein concentrations. The minimum molecular weight as determined by Sephadex G-200 chromatography is around 67 000.

Absorbance and fluorescence spectra show that neither DPNH nor adenosine diphosphate ribose is bound to the enzyme.

The bee enzyme differs from the crystalline rabbit-muscle enzyme in electrophoretic, ultracentrifugal, and immunological properties.

• 1.

  1. The distribution of aldose-reducing activities was studied in several rabbit organs. Although all the organs studied had the ability to use NADPH as a cofactor for the reduction of xylose, the different substrate specificities observed suggest that the activity may be due to the presence of at least two different enzymes. These were aldose reductase (polyol:NADP⁺ oxidoreductase, EC 1.1.1.21), in lens, adrenal and skeletal muscle and NADP⁺-L-hexonate dehydrogenase (L-gulonate:NADP⁺ oxidoreductase, EC 1.1.1.19) in liver, kidney, heart, spinal cord and brain.

• 2.

  2. Calf lenses were dissected into three portions: capsule (including the epithelium), cortex and nucleus, and the concentrations of aldose reductase, galactokinase, (ATP:D-galactose 1-phosphotransferase, EC 2.7.1.6) and glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP⁺ oxidoreductase, EC 1.1.1.49) were determined in the soluble fractions of the extracts. The distribution patterns were different for the three enzymesl the ratio cortex:epithelium:nucleus was 1:21:1.1 for aldose reductase; 1:3:0.02 for galactokinase and 1:7:0.04 for glucose-6-phosphate dehydrogenase.

• 3.

  3. When calf lenses were incubated in media containing galactose, the accumulation of dulcitol was greatest in the epithelial region and least in the nucleus with an intermediate amount in the cortex.

• 4.

  4. No biosynthesis of ascorbate from either D-[6-¹⁴C]glucuronate or D-[6-¹⁴C]-glucuronolactone could be demonstrated in incubated rabbit lens. However, there was conversion of the labeled carbon to CO₂ and some accumulation of labeled L-gulonate. Aldose reductase, although it reduces glucuronate to L-gulonate, does not appear to be involved in ascorbate biosynthesis.