Effect of pH, ionic strength and univalent inorganic ions on the reconstitution of aspartate aminotransferase

1. The effect of pH change on the reconstitution of aspartate aminotransferase (EC 2.6.1.1), i.e. the reactivation of the apoenzyme with coenzyme (pyridoxal phosphate and pyridoxamine phosphate), was studied in the pH range 4.2–8.9 by using three buffer systems at concentrations ranging from 0.025 to 0.1m. 2. Although the profile of the reconstitution rate–pH curve in the range pH5.2–6.8 (covered by sodium cacodylate–HCl buffer) reflects the influence of the H+ concentration on the reconstitution process, the profile of the curve in the pH ranges 4.2–5.6 and 7.2–8.25 (covered respectively by sodium acetate–acetic acid and Tris–HCl buffers) appears to be influenced by the ionic strength of the buffer. 3. The reconstitution is also influenced by univalent inorganic ions such as halide ions and, to a lesser extent, alkali metal ions, which are known to alter the water structure.

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The mechanism of plasticization of the abdominal cuticle in Rhodnius

Journal of Experimental Biology ◽

10.1242/jeb.62.1.81 ◽

1975 ◽

Vol 62 (1) ◽

pp. 81-98

Author(s):

SE Reynolds

Keyword(s):

Ionic Strength ◽

Inorganic Ions ◽

Ph Change ◽

Test Conditions

1. The mechanism of plasticization of the abdominal cuticle in Rhodnius larvae has been investigated, using the properties of loops of cuticle under varying test conditions as a model for the behaviour of the cuticle in vivo. 2. It is supposed that plasticization is effected by a change in the intracuticular environment. A number of model mechanisms for plasticization may be proposed, which suppose that the epidermis is capable of regulating (a) pH, (b) ionic strength,(c) Ca and/or Mg, (d) urea, within the cuticle. 3. Analyses of cuticle ash show that models(b) and (c) are not responsible for plasticization in vivo. The levels of inorganic ions within the unplasticized cuticle are not sufficiently high to allow plasticization upon their removal. 4.No evidence for model (d) has been found; urea does not occur in the cuticle in detectable quantities. 5. Exact measurements of the intracuticular pH have not been achieved but straining experiments strongly suggest that a change in pH occurs within the cuticle on plasticization. This pH change is probably large enough to account for the increased extensibility shown by plasticized cuticle.

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Part of the phospho group of pyridoxal phosphate may titrate over the pH range 5-8 in aspartate aminotransferase

Biochemical Journal ◽

10.1042/bj2800832 ◽

1991 ◽

Vol 280 (3) ◽

pp. 832-833

Author(s):

H B F Dixon

Keyword(s):

Aspartate Aminotransferase ◽

Pyridoxal Phosphate ◽

Ph Range

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Effect of pH and NH4NO3 as a Spray Additive on Penetration of NAA Through Isolated Tomato Fruit Cuticle

HortScience ◽

10.21273/hortsci.33.3.550a ◽

1998 ◽

Vol 33 (3) ◽

pp. 550a-550 ◽

Cited By ~ 1

Author(s):

Royal G. Fader ◽

Martin J. Bukovac

Keyword(s):

Direct Measurement ◽

Sodium Citrate ◽

Tomato Fruit ◽

Initial Slope ◽

Control Effect ◽

Solution Ph ◽

Ph Change ◽

Effect Of Ph ◽

Spray Droplets ◽

Partition Behavior

We have reported that NH4NO3 (AN, 8 mM, pH 4.2), applied as simulated spray droplets, enhanced penetration of 14C-NAA through isolated leaf and fruit cuticles. One explanation for this response is that AN depresses NAA (pKa= 4.2) dissociation, increasing the nondissociated moiety, which penetrates more readily than the anion (NAA'). Direct measurement of AN (concn. 0-800 mM) effect on NAA (215 μM) dissociation as indexed by change in solution pH revealed no significant effect, with a pH change from 4.19 to 4.05. This change is not sufficient to account for the observed enhancement. When 14C-NAA, buffered (20 mM sodium citrate) at pH 3.2, 4.2, 5.2, 6.2, was partitioned against chloroform, there was a marked increase in NAA partitioning into chloroform as pH was decreased. AN (8 mM) did not alter this partition behavior, also indicating no effect on NAA dissociation. However, in cuticle penetration studies, using a finite dose system with 14C-NAA buffered at pH 3.2, 4.2, 5.2, 6.2, and in the presence and absence of 8 mM AN, there was no marked or consistent pH or AN (-70 to + 232 % of no AN control) effect on penetration as indexed by initial slope (4-12 h) or penetration after 120 h. The possible effects of AN and buffer on penetration of 14C-NAA from the droplet deposit will be discussed.

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A Class of Drugs that Inhibits Platelet Release and Aggregation by Apparent Interference with Anion Transport

10.1055/s-0039-1684478 ◽

1979 ◽

Author(s):

N.R. Shulman ◽

H.B. Pollard ◽

K. Tack-Goldman

Keyword(s):

Pyridoxal Phosphate ◽

Human Platelets ◽

Anion Transport ◽

Serotonin Release ◽

Secretory Cells ◽

Chloride Uptake ◽

Potential Alternative ◽

Osmotic Lysis ◽

Platelet Release ◽

Ph Range

The platelet release reaction is analogous to the process of exocytosis by which many other secretory cells release hormones or mediators from intracellular granules. Anion transport blocking (ATB) drugs Inhibit release of epinephrine from isolated chromaffin granules (CG) by blocking chloride uptake and preventing osmotic lysis. Studies on platelets analagous to those done on CG showed that increasing osmotic strength in the range 600-1000 m0sm progressively suppressed serotonin release to completion and that ATB drugs (viz, probenecid, SITS, pyridoxal phosphate and suramin) at mM concentrations completely inhibited release and aggregation of human platelets stimulated by thrombin, ADP, A23187, epinephrine or collagen. Sulfinpyrazone has the appropriate structure for anionic blocking, and may suppress platelet function as effectively by this mechanism as by cycloxy-genase inhibition. The ATB drugs acted apparently to prevent movement of OH- from the more alkaline medium into the relatively acidic granule, for platelet release was not inhibited by replacing anions with isethionate or sucrose, but was markedly dependent on OH- in the pH range 6 to 7.5 where inhibition by the ATB drugs was competitive with respect to OH-. Since the ATB compounds include some relatively nontoxic drugs in common use, and since their action on platelets differs markedly from that of aspirin, they should receive attention as potential alternative or auxiliary antithrombotic agents.

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