Some properties of acid protease from the thermophilic fungus, Penicillium duponti K1014

A purified acid protease from a true thermophilic fungus, Penicillium duponti K1014, was most active at pH 2.5 for milk casein and at pH 3.0 for hemoglobin. The enzyme was stable at a pH range of 2.5 to 6.0 at 30 C for 20 h. The acid protease retained full activity after 1 h at 60 C at a pH range between 3.5 and 5.5. At the most stable pH of 4.5, more than 65% of its activity remained after heat treatment for 1 h at 70 C. These thermal properties show the enzyme as a thermophilic protein. The enzyme activity was strongly inhibited by sodium lauryl sulfate and oxidizing reagents such as potassium permanganate and N-bromosuccinimide. No inhibition was caused by chelating reagents, potato inhibitor, and those reagents which convert sulfhydryl groups to mercaptides. Reducing reagents showed an activating effect. The enzyme showed the trypsinogen-activating property at an acidic pH range; optimal trypsinogen activation was obtained at a pH of approximately 3.0. The isoelectric point of the enzyme was estimated to be pH 3.89 by disk electrofocusing. By using gel filtration, an approximate value of 41,000 was estimated for the molecular weight.

Characterization and partial purification of the acetylcholine receptor from Torpedo electroplax

Binding of acetylcholine in the concentration range 1 nM-1 muM was measured by equilibrium dialysis to a particulate preparation of Torpedo electroplax, without or with prior treatment of the tissue with one of three chemical modifying reagents. Significant reduction in binding of acetylcholine resulted after treatment with 1,4-dithiothreitol, p-chloromercuribenzoate, or p-(trimethylammonium)-benzenediazonium fluoroborate. Partial reversal of the reduction in binding occurred when dialysis was performed in the presence of 5,5'-dithiobis-(2-nitrobenzoic acid) or potassium ferricyanide (in the case of treatment with dithiothreitol), and 2-mercaptoethanol (in the case of treatment with p-chloromercuribenzoate). It is concluded that the functional acetylcholine-receptor macromolecule of Torpedo electroplax has disulfide bond(s), sulfhydryl group(s), and one or more of the amino acids vulnerable to diazotization by p-(trimethylammonium)-benzenediazonium fluoroborate. This, plus the effect of phospholipase C (EC 3.1.4.3) in elimination of detectable binding of acetylcholine after electrofocusing, is additional evidence that the functional acetylcholine receptor is a phospholipoprotein or a phospholipid-protein complex, which has a low isoelectric point of 4.5 +/- 0.2, yet is denatured by exposure to low pH for 24 hr. Due to this adverse effect, recovery of binding of acetylcholine after electrofocusing, as detected by equilibrium dialysis or ultrafiltration, is only 23% and, so far, only 6.3-fold purification of functional acetylcholine receptors by this technique is possible. Three or two forms of acetylcholinesterase (EC 3.1.1.7), whose peaks have isoelectric points ranging from 4.3 to 7.2, appear after electrofocusing of Torpedo extracted with 1% Triton X-100 or Lubrol, respectively. The major peak in either preparation has an isoelectric point of 5. Although the peaks of the functional acetylcholine receptors and of acetylcholinesterase of Torpedo electroplax are separable by electrofocusing, it has not been possible to isolate fractions that contain functional receptors but that are free of acetylcholinesterase. The opposite is possible.

Inhibition of peroxidase by methanol and by methanol-nitroferricyanide for use in immunoperoxidase procedures

The cytochemical reaction for peroxidase is partially inhibited by methanol. The addition of a small amount of sodium nitroferricyanide to the absolute methanol causes further inhibition. The activity of peroxidase is completely suppressed by methanol containing 1% sodium nitroferricyanide and l% acetic acid. The antibody to horseradish peroxidase is much less affected by these inhibitors than horseradish peroxidase itself. By using appropriate combinations of these inhibitors and by varying the time or temperature of treatment, the activity of injected horseradish peroxidase, or of endogenous peroxidase in leukocytes, erythrocytes or normoblasts, can be much decreased or suppressed while the specific ability of the antibody to adsorb horseradish peroxidase can be preserved to a considerable extent. KCN and NaN3 inhibit peroxidase activity only moderately under conditions required for immunoperoxidase procedures, i.e., after removal of the inhibitors.

An atypical substrate-inhibitor-rate relationbship for the action of antimycin A on the succinate-ferricyanide reductase activity of beef heart electron transfer particles

The degree of inhibition of the succinate–ferricyanide reductase activity of beef heart electron transfer particles by antimycin A is negligible at low succinate concentrations (< 1 mM) but increases to about 40% at saturating concentrations of succinate. This behavior is explained on the basis of a random order mechanism for the primary dehydrogenase with alternative routes from the monosubstrate complexes, only one of which is sensitive to antimycin.

Bacteriology of manganese nodules. V. Effect of hydrostatic pressure on bacterial oxidation of MnII and reduction of MnO2

It was experimentally demonstrated that two strains of Arthrobacter 37, one growing at 25 C and the other at 5 C, could catalyze Mn(II) oxidation at hydrostatic pressures well in excess of the pressure encountered by the parent culture in its original habitat in the ocean (80 atm). The strain grown at 5 C showed an increase in temperature optimum for manganese oxidation with increase in pressure. It was like-wise experimentally shown that induced Bacillus 29 without added ferricyanide and uninduced Bacillus 29 with added ferricyanide could catalyze MnO(2) reduction at hydrostatic pressures in excess of the pressure encountered by this organism in its original habitat (187 atm). The uninduced Bacillus 29, in the presence of ferricyanide, was active over a wider range of pressures (1 to 1,000 atm) than the induced Bacillus 29 in the absence of ferricyanide (1 to 467 atm). At corresponding pressures, the uninduced culture was also considerably more active than the induced culture. Special techniques were developed for measuring Mn(II)-oxidizing and MnO(2)-reducing activity under pressure.

Oxidative degradation of dihydrofolate and tetrahydrofolate

7,8-Dihydrofolate has been degraded oxidatively using ferricyanide under anaerobic conditions. Three reaction pathways have been found for this oxidation, and these pathways can be controlled by variation of the pH and by the nature of the buffer anion. At pH 9, treatment of dihydrofolate with two equivalents of ferricyanide leads to quantitative formation of folate. At pH 5.6 in morpholinoethanesulfonic acid buffer, the same reactants produce p-aminobenzoylglutamate, dihydroxanthopterin, and formaldehyde. Each of these products has been identified, and isolated in high yield. 6-Formyldihydropterin can be isolated by oxidation of dihydrofolate in either phosphate or carboxylic acid buffers. This compound does not appear to be an intermediate in the formation of dihydroxanthopterin under the conditions of our experiments. Tetrahydrofolate was also degraded oxidatively using ferricyanide. Although it is more susceptible to cleavage than is dihydrofolate, tetrahydrofolate gives similar products. In addition, moderate quantities of pterin were isolated from oxidation of tetrahydrofolate at pH 5.6.