The mycotoxin, aflatoxin B₁, elaborated by the fungus Aspergillus flavus is a coumarin-type compound. This compound has previously been reported in the literature to have an effect on rat liver mitochondria, although the reports are inconsistent. The effect of this compound on oxygen consumption by rat liver mitochondria was examined potentiometrically. All experiments were carried out below the critical micelle concentration of aflatoxin B₁ which was determined in the oxygen electrode solution of Estabrook to be 0.48 mM. Mitochondria were isolated from 80-150 g male Sprague-Dawley derived rats. Aflatoxin B₁ at a concentration of 0. 48 mM was found to inhibit oxygen consumption by 43% in the presence of ADP and by 63% in the presence of DNP. The inhibition brought about by 0.48 mM aflatoxin B₁ occurs when either succinate or β-hydroxybutyrate is used as a substrate. When electrons were fed into the electron transport chain at cytochrome c₁ (or c) using TMPD and ascorbate no inhibition was observed. TMPD, however, released the inhibition brought about by 0.48 mM aflatoxin B₁ in the presence of succinate or β-hydroxybutyrate as substrates. No relief of the inhibition was obtained with menadione. The site of inhibition appears to be between cytochrome b and cytochrome c₁ (or c). The ADP:0 ratio was also depressed by 35% in the presence of 0.48 mM aflatoxin B₁ when NAD-dependent substrates were employed.
Mitochondria from protein deficient animals were found to be 42% less sensitive to inhibition by aflatoxin B₁ than mitochondria from protein sufficient animals. The ADP:0 ratio with NAD-dependent substrates was found to be 37% less sensitive in mitochondria from protein deficient animals than in protein sufficient animals.
Gregg particles were prepared from mitochondria isolated from protein deficient as well as protein sufficient animals. Both types of submitochondrial particles were found to be more sensitive to aflatoxin B₁ than the whole mitochondria. It was concluded that the inhibition was limited in whole mitochondria by the inner mitochondrial membrane; and in protein deficient mitochondria there is an alteration in the inner mitochondrial membrane which makes aflatoxin B₁ a less potent inhibitor of electron flow.
The fact that the inhibition occurs in the presence of DNP as well as ADP indicates that the inhibition is in the electron transport chain and not in the phosphorylating functions ancillary to the chain. DNPstimulated ATPase activity was only slightly affected by aflatoxin B₁ in the absence of reducing substrates. DNP-stimulated ATPase activity was however markedly reduced in the presence of reducing substrate and aflatoxin B₁. This supports the contention that aflatoxin B₁ effects electron transport in the chain and not in the phosphorylating functions ancillary to the chain though some effect is seen there also. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/77843 |
| Date | January 1972 |
| Creators | Doherty, William Paul |
| Contributors | Biochemistry and Nutrition |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | x, 91 leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 39979517 |
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