HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Detwiler, T. C. Articles by Nason, A. Search for Related Content PubMed PubMed Citation Articles by Detwiler, T. C. Articles by Nason, A. Social Bookmarking                      What's this?

Effects of Digitonin and Tocopherol on Bovine Heart Muscle Reduced Diphosphopyridine Nucleotide- and Succinate-Cytochrome c Reductase and Cytochrome c Oxidase

From the ¹ From the McCollum-Pratt Institute, The Johns Hopkins University, Baltimore, Maryland 21218

The effects of digitonin and tocopherol on bovine heart reduced diphosphopyridine nucleotide- and succinate-cytochrome c reductases and cytochrome c oxidase have been studied with the following results.

1. Low concentrations of digitonin stimulate succinate- and DPNH-cytochrome c reductase and cytochrome c oxidase. Higher concentrations of digitonin completely inhibit cytochrome c reductases, while continuing to stimulate cytochrome c oxidases.

2. Inhibition of the reductases is reversed by either dilution or addition of tocopherol. Stimulation of the reductases and oxidase is prevented by tocopherols but is not reversed by either tocopherols or dilution.

3. Of other compounds tested for ability to prevent these digitonin effects, -tocopherol polyethylene glycol succinate 1000 and coenzyme Q₄ chromanol were effective with a soluble preparation of DPNH-cytochrome c reductase. In addition to these, -tocopheryl succinate and -tocopheryl phosphate were effective with a particulate preparation of succinate-cytochrome c reductase. -Tocopheryl succinate, -tocopheryl phosphate, -tocopheryl hydroquinone, and vitamin D₂ prevented the stimulation of cytochrome c oxidase.

4. Digitonin stimulation of succinate-cytochrome c reductase is associated with increases in both V_max and K_m (succinate); digitonin inhibition is associated with decreases in both V_max and K_m (succinate).

5. Reduced with respect to oxidized difference spectra of normal and inhibited preparations indicated succinate reduction of cytochromes a + a₃, b, and c₁, and of flavin in the normal enzyme, but almost no reduction of flavin and cytochromes of a digitonin-inhibited enzyme.

6. Digitonin caused almost complete inhibition of enzymatic reduction of ferricyanide by succinate, but only partial inhibition of reduction of indophenol and phenazine methosulfate. It is concluded from this and from the spectral studies that inhibition is before cytochrome b and after, or at, the flavin.

7. Digitonin stimulates both the reduction or oxidation of cytochrome c but not the reduction of ferricyanide. It is concluded that stimulation is due to irreversible changes in the enzyme that permit more rapid reaction of soluble cytochrome c with the particulate enzyme.

8. Tocopherol apparently forms an insoluble complex with digitonin and decreases the concentration of digitonin in solution. This is possibly the mechanism by which tocopherol counteracts the effects of digitonin on enzymes. Other compounds known to combine with digitonin do not decrease the concentration of digitonin under the conditions of the enzyme assays.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?