Rat liver homogenates

D-Mevalonic acid is the fundamental intermediate in the biosynthesis of the terpenoids and steroids, together classed as poly-isoprenoids. The biogenetic isoprene unit is isopentenyl pyrophosphate which arises by enzymic decarboxylation-dehydration of mevalonic acid pyrophosphate. D-Mevalonic acid is almost quantitatively incorporated into cholesterol synthesized by rat liver homogenates. 

Bicker and Fischer incubated ephedrine isomer 127 with a rat liver homogenate to which ATP and sulfate were added [191]. Formation of aziridine 128, requiring... 

Figure 11.22 Biochemical formation of aziridines in rat liver homogenate.

Comporti, M., Saccocci, C. and Dianzani, M.U. (1965). EfiFect of carbon tetrachloride in vitro and in vivo on lipid peroxidation of rat liver homogenates and subcellular fractions. Enzymologja 29, 185-204. 

Rupp and Locker3 Rat liver Homogenized in a solution containing SDS, and proteinase K Not available, using hybridization including dot-blot method RNA purified from FFPE tissue is suitable for hybridization. 

Tumorigenicity of tetrahydroepoxides. As yet, only Ch H -epoxide has been directly demonstrated to be tumorigenic (18). However, indirect evidence has been found in the high tumorigenicity of 3,4-dihydro BA, 9,10-dihydro BeP and 3,4-dihydrobenz[c]acridine (19-21), each of which is a likely metabolic precursor of a bay-region H -epoxide. In the case of 9,10-dihydro BeP, cis- and trans-9,10-dihydroxy -9,10,11,12-tetrahydro BeP were identified as products of metabolism of 9,10-dihydro BeP (22), and are the expected products of hydration of the epoxide. Diols are also formed from 7,8-dihydro BaP upon metabolism with prostaglandin endoperoxide synthase (23) or with rat liver homogenates (24). 

The mutagenicity of benzofa]pyrene for bacteria was demonstrated by Ames et al. (60) They found that in the presence of rat liver homogenates benzo[a]pyrene induced both frameshift and base-pair substitution mutations. When the chemistry of benzo[a]pyrene activation had been worked out and the ultimate carcinogenic form identified as a diolepoxide, BPDE (reviewed in 61-62), several investigators (63-66) showed that BPDE was an extremely potent mutagen, also capable of inducing both frameshift and base-pair substitution mutations. 

The assay can be performed using mutagenic substances that react directly with DNA or, where metabolic activation is necessary, with pre-mutagen in the presence of rat liver homogenate that is enriched in mixed function oxidases (termed S9). Metabolic oxidation (if that is what is required) results in ultimate or penultimate mutagenic forms, which act as electrophiles towards S. typhimurium. 

Species extrapolation. No species extrapolation was attempted in this model. Results from in vitro studies in rat liver homogenates were used to estimate kinetic parameters for the catabolism of n-hcxane and synthesis of 2,5-hexanedione. 

During a 30 minute incubation period, low levels of aldrin epoxidation (30-150 picomoles dieldrin/mg protein) were measured compared to those observed using enzyme sources such as aquatic Trichoptera Limnephilus sp. gut homogenates (1 pmole/mg protein 28) or rat liver homogenates (3000 pmoles/mg protein unpublished) under similar incubation conditions. Anisole metabolism based upon substrate disappearance was detectable but less than 5 picomoles/mg protein were transformed during the incubation period. Characteristics of the enzyme system are incompletely described owing to the low and variable levels of activity which have been obtained. 

Methylation in both ortho-positions on the aniline ring appears to impede hydrolysis of the amide bond. Thus, 2,4,6-trimethylacetanilide (4.105) was not hydrolyzed by rat liver homogenates, perhaps due to steric hindrance by the 2- and 6-Me groups [71]. Similarly, the amide bond of the hypocholes-terolemic agent 2,2-dimelhyl-A-(2,4,6-trimethoxypheiiyl )dodccanamidc... 

Four/V-[(acyloxy)methyl] derivatives of 5-FU (8.152, R = AcOCH2, Et-COOCH2, PrCOOCH2, and (7-Bu)COOCH2) were very stable in buffer at pH 7.4 and 37° (t1/2 70, 90, 140, and 700 h, respectively) [219], In 80% human plasma under the same conditions of pH and temperature, the f1/2 values were 14, 9.6, 2.3, and 40 h, respectively, i.e., a marked substrate-dependent acceleration. In rat liver homogenates, the tm values for decomposition were in the order of a few minutes or less. Clearly enzymatic hydrolysis is possible for such compounds and may even be quite significant. Additional data on A-[(acyloxy)methyl] prodrugs have confirmed their potential for topical delivery of 5-FU [220],... 

One case where enzymatic involvement is documented is that of (R)-a-fluoro-/3-alanine (11.42), itself the major (>80%) metabolite of 5-fluoroura-cil (11.16) in humans. With rat liver homogenates, it was demonstrated that mitochondrial L-alanine-glyoxylate aminotransferase II (AlaAT-II, EC 2.6.1.44) catalyzed the defluorination of (R)- and (S)-a-fluoro-/3-alanine with catalytic efficiencies of 0.038 and 0.050 mM"1 s 1 at 37° and pH 7.0, respectively, [76], The primary product of the reaction was jS-aminoacrylate... 

Rubinstein D, Kanics L. 1964. The conversion of carbon tetrachloride and chloroform to carbon dioxide by rat liver homogenates. Can J Biochem 42 1577-1585. 

The isolation of an SCP protein from rat liver homogenates has also been reported (S2). This protein has been found to be heat-labile, to be detectable only in the liver, and to have a molecular weight of approximately 50,000 daltons by gel filtration (S2) and 28,000 daltons by sedimentation equilibrium (S3). Although the functional properties of the heat-labile SCP (SI) are similar to the heat-stable SCP (R2, R3), these proteins appear to be different. According to Scallen et al. (S3), their SCP preparation resembles chemically serum LDL this based on the similarity in amino acid composition between these two proteins. In the... 

With fresh rat liver homogenates that were not fortified with UDP-sugar, appreciable conjugate formation of bilirubin occurred (HIO, M5). The process occurred in the absence of added Mg-+ and was inhibited by digitonin (HIO). The conjugation rates at 37°C were constant for the first 3- to 5-minute period, then decreased gradually to zero (M5). 

C9. Cooke, B. A., and Taylor, W., The metabolism of progesterone by animal tissues in vitro. 4. Conjugate formation during the metabolism of (4- C) progesterone by female-rat liver homogenate. Biochem. J. 86, 365-371 (1963). 

To study the mechanism of cytotoxic action of CNT we used a modified method of spin labels [20], which allows the quantitative determination of CNT influence on membrane integrity of human blood erythrocytes, and mitochondrial activity of hepatocytes in rat liver homogenate, without extraction of mitochondria from cells. 

The exact mechanism underlying the carcinogenesis is less clear, but presumably involves inhibition of RNA synthesis or the production of abnormal ethylated nucleic acids and hence disruption of transcription, translation, or possibly replication. It is of interest that ethionine is not mutagenic in the Ames test, with or without rat liver homogenate. However, ethionine may be carcinogenic after metabolism to vinyl homocysteine (in which vinyl replaces ethyl), which is highly mutagenic. 

When this compound was incubated with rat-liver homogenates, only the cysteinyl-glycine conjugate was found (lARC, 1976). 

FIGURE 15-33 Dependence of glycolytic flux in a rat liver homogenate on added enzymes. Purified enzymes in the amounts shown on... 

C]acetyl-CoA is added to a rat liver homogenate that is synthesizing cholesterol, where will the 14C label appear in A3-isopentenyl pyrophosphate, the activated form of an isoprene unit ... 

Niwaguchi et al. (14-16) reported that when rat liver homogenates were incubated in a system containing 14C-L-glutamate, glucose, DPN, adenosine triphosphate (ATP), magnesium ions, cytochrome c, and fu-marate, an acidic compound was formed which could be identified as pyrrolidone carboxylic acid by infrared spectroscopy, electrophoresis,... 

Kulkybaev GA, Merkusheva NV. 1992a. Dynamics of the activity of NAD-dependant isocitrate dehydrogenase in rat liver homogenate under the effects of harmful substances in the phosphoms industry. Gig Tr Prof Zabol 0( 1) 21-23. 

TRAP with luminol and 0.2 mM luminol, 10 mM ABAP in Chemiluminescence, induction Rat liver homogenate ... 

---