Rat Liver Mitochondrial Preparations Research Articles

Modalités d'action d'un système de raccourcissement de l'acide érucique au niveau des mitochondries de foie de rat

In this work, were studied the conditions of erucic acid (cis-docosenoic, n-9) shortening by using Rat liver mitochondrial preparations which were incubated in vitro with [14-14C] erucic acid (22:1), with inhibitors of the respiratory chain (rotenone, cyanide) or not, with activators of either the shortening reaction (NAD+, NADP+), or beta-oxidation (malate, carnitine, cytochrome c) or not. The shortening activity was measured by the amount of 14C radioactivity recovered in the shorter fatty acids formed (20:1, 18:1, 16:1) when beta-oxidation was inhibited. The beta-oxidation activity was measured by the amount of 14C recovered in the acid-soluble products (P A S). The incubations were performed under conditions which were the least favourable to peroxysomal activity. Data showed that, with increasing amounts of albumin, which inhibits peroxysomal activity, increasing amounts of shorter fatty acids (20:1, 18:1, 16:1) were formed from erucic acid. This shortening reaction was strongly stimulated by NAD+, more than by NADP+; it was also stimulated by cytochrome c and much more when both NAD+ and cytochrome c were added. Similar data were observed in beta-oxidation, except that practically NADP+ did not exhibit any stimulating effect. Oxidation of NADH by mitochondria only occurred when cytochrome c was added to the medium and was not modified by the addition of ADP or rotenone. These data show that liver mitochondria are capable of shortening erucic acid, as are peroxysomes. This shortening reaction is highly NAD+-dependent and seems to be localized outside the matrix. This system could constitute a second route for utilization of fatty acids in mitochondria, besides the well-known path of beta-oxidation.

Metabolism of malonaldehyde in vivo and in vitro.

The metabolism of malonaldehyde (MA) was investigated in vivo using male Wistar rats and in vitro using rat liver mitochondria. Twelve hr after intubation with [1,3-14C] MA, 60-70%, 5-15% and 9-17% of administered radioactivity was recovered in expired CO2, feces and urine, respectively. In rats intubated with [1,2-14C) acetate, the corresponding values were 68-82%, 1-2% and 2.3%. 14CO2 evolution was initially slower after 14C-MA administration than after 14C-acetate administration and more radioactivity was excreted in the feces and urine. In vitro experiments using [1,3-14C] MA showed that MA is metabolized primarily in the mitochondria via reactions involving O2 utilization and 14CO2 production. The apparent Km and Vmax were 0.5 mM and 9.3 nmol/min/mg protein for O2 uptake, respectively, and 2.0 mM and 2.4 nmol/min/mg protein for 14CO2 production. Addition of malonic acid to mitochondrial incubates at concentrations inhibitory to succinate dehydrogenase did not affect MA-induced O2 uptake but enhanced 14CO2 production from 14C-MA. 14C-Acetate appeared to be the major accumulating metabolite in rat liver mitochondrial preparations following a 120-min incubation with 14C-MA. A probable biochemical route for MA metabolism involves oxidation of MA by mitochondrial aldehyde dehydrogenase followed by decarboxylation to produce CO2 and acetate.

3] Large-scale preparation of rat liver mitochondria in high yield

Preparation of mitochondrial components requires large quantities of mitochondria. This chapter describes a procedure for large-scale isolation of rat liver mitochondria in high yield. Mitochondria are recovered from the nuclear fraction and the postnuclear supernatant. The chapter discusses the characterization and yield of the mitochondria. The recovery of mitochondria (both mitochondria R1 and R2) is approximately two-thirds of the amount estimated to be in the liver. Mitochondria R1 are intact and are mainly in the condensed configuration. They approach ultimate purity, as judged by electron microscopy and analysis using marker enzymes. They are practically devoid of contamination by other organelles, such as endoplasmic reticulum, plasma membranes, peroxisomes, and lysosomes, which contaminate mitochondria R2. Mitochondria R2 are estimated to be 80–85% pure. The major contamination, about 10–15%, is by endoplasmic reticulum.

A high-yield preparative method for isolation of rat liver mitochondria

A differential centrifugation method for the preparation of rat liver mitochondria is described, which results in final mitochondrial yields of at least 35 to 40 mg of mitochondrial protein per gram wet weight of liver. These mitochondria are shown to be functionally and ultrastructurally intact. They exhibit acceptor control ratios of 6 to 8 and ADP O ratios near 2.0 with succinate as a substrate. In addition, they appear homogeneous by electron microscopy criteria. This method can be used to prepare rat liver mitochondria in high yield on either a large- or a small-scale basis.

Uptake of hydroxocobalamin by rat liver mitochondria. Binding to a mitochondrial protein.

Lysosome-free preparations of rat liver mitochondria take up hydroxo[57Co]cobalamin by a process which is dependent on mitochondrial swelling, rather than on energy or ion fluxes. The uptake system is saturable and unidirectional, leading to inside/outside concentration ratios of 17. The process also exhibits specificity: cyano[57Co]cobalamin is taken up less rapidly and to a lesser extent than hydroxocobalamin; methylcobalamin and adenoslcobalamin inhibit hydroxocobalamin uptake markedly, while cyanocobalamin does not. The [57Co]cobalamin ([57Co]Cbl) taken up is bound to a mitochondrial protein whose apparent molecular weight is 120,000 by Sephadex G-150 chromatography. Double reciprocal plots of bound [57Co]Cbl versus medium [57Co]Cbl concentration yield estimates for bound Cblmax of 29 pmol/mg of protein and for Kd is 8.2 muM. We conclude that mitochondrial uptake of cobalamins occurs via the diffusion of free cobalamins into the mitochondria and their subsequent binding to a high affinity mitochondrial protein(s) which we propose to be the source of the unidirectional character, the saturability, and the specificity of the uptake system.

Isolation of L-dynurenine 3-hydroxylase from the mitochondrial outer membrane of rat liver.

Outer membrane preparations of rat liver mitochondria were isolated, after the mitochondria had been prepared by mild digitonin treatment under isotonic conditions. L-Kynurenine 3-hydroxylase [EC 1.14.13.9] was solubilized on a large scale from outer membrane by mixing with 1% digitonin or 1% Triton X-100, followed by fractionation into a minor fraction I and a major fraction II by DEAE-cellulose column chromatography. The distribution of total L-Dynurenine 3-hydroxylase was roughly 20 and 80% in fraction I and II, respectively. Fraction I consisted of crude enzyme loosely bound to anion exchanger. In the present investigation, fraction I was not used because of its low activity and rapid inactivation. In contrast, fraction II consisted of crude enzyme with high activity, excluded from DEAE-cellulose column chromatography in the presence of 1 M KC1. In addition, fraction II was purified by Sephadex G-200 gel filtration and DEAE-Sephadex A-50 column chromatography with linear gradient elution, adding 1 M KC1 and 1% Triton X-100 to 0.05 M Tris-acetate buffer, pH 8.1. After isoelectric focusing, the purified enzyme preparation was proved to be homogeneous, since the L-kynurenine 3-hydroxylase fraction gave a single band on disc gel electrophoresis. The molecular weight of this enzyme was estimated to be approximately 200,000 or more by SDS-polyacrylamide gel electrophoresis and from the elution pattern on Sephadex G-200 gel filtration. A 16-Fold increase of the enzyme activity was obtained compared with that of the mitochondrial outer membrane. The isoelectric point of the enzyme was determined to be pH 5.4 by Ampholine isoelectric focusing.

In vitro synthesis of guanosine polyphosphates in rat liver mitochondrial preparations.

In vitro synthesis of guanosine polyphosphates in rat liver mitochondrial preparations.

Adenosine triphosphatase from rat liver mitochondria: Separate sites involved in ATP hydrolysis and in the reversible, high affinity binding of ADP

Homogeneous ATPase from rat liver mitochondria binds one mole of ADP per mole of enzyme reversibly, and with high affinity (K D = 1–2 μM). The high affinity binding site is highly specific for ADP and dADP. AMP does not bind. Agents which inhibit ATP hydrolysis have little inhibitory effect on the high affinity binding of ADP. These agents include adenylyl imidodiphosphate (AMP-PNP), azide, sucrose, and the divalent cation Mg ++. AMP-PNP inhibits ATPase activity in phosphorylating membrane preparations of rat liver mitochondria by about 90 percent, but is without effect on ATP synthesis. These results are consistent with the view that the purified soluble, and the membrane-bound ATPase of rat liver mitochondria contain separate sites involved in ATP hydrolysis and in the reversible, high affinity binding of ADP.

Biosynthesis of bis(monoacylglyceryl)phosphate and acylphosphatidylglycerol in rat liver mitochondrial.

Bis(monoacylglyceryl)phosphate is present in trace quantities in normal liver where it represents smaller than 1 percent of total liver phospholipids. This compound is of considerable interest since its level can be greatly increased in certain lipidoses, either of a genetic nature or caused by drugs. Biosynthesis of bis(monoacylglyceryl)P in vitro has not previously been demonstrated. This paper reports the enzymatic formation of bis(monoacylglyceryl)P and acylphosphatidylglycerol as minor products from cytidine diphosphate diglyceride and radioactive sn-glycerol-3-P using a crude mitochondrial fraction from normal rat liver; phosphatidylglycerol was the principal product. Evidence is also presented which shows the enzymatic formation of acylphosphatidylglycerol and bis(monoacylglyceryl)P from [1',3'-14C]phosphatidylglycerol by a crude rat liver mitochondrial preparation in vitro. The structures of the radioactive bis(monoacylglyceryl)P and acylphosphatidylglycerol were tentatively established by thin layer chromatography, and chromatography of the products of mild alkaline hydrolysis and acetolysis. Radioactive acylphosphatidylglycerol was stoichiometrically converted to bis(monoacylglyceryl)P by treatment with bee venom phospholipase A, providing additional evidence for the structure of acylphosphatidylglycerol and bis(monoacylglyceryl)P.

Effect of Fusarium sporotrichiella v. sporotrichioides mycotoxin on membranes of subcellular particles

We have studied the in vitro action of various concentrations of sporofusarin (mycotoxin produced by Fusarium sporotrichiella v. Sporotrichioides) on the total and non-sedimentable supernatant activity of enzymes in isolated preparations of rat liver mitochondria, lysosomes and microsomes. The activity of the following enzymes was investigated: succinate dehydrogenase (EC 1.3.99.1), cytochrome c oxidase (EC 1.9.3.1), malate dehydrogenase (EC 1.1.1.37), acid RNAase (EC 3.1.4.22), arylsulphatases A and B (EC 3.1.6.1.), β-glucuronidase (EC 3.2.1.31), β-galactosidase (EC 3.2.1.23), β-glucosidase (EC 3.2.1.21), β- N-acetylglucosaminidase (EC 3.2.1.30), α-galactosidase (EC 3.2.1.22), α-mannosidase (EC 3.2.1.24), glucose-6-phosphatase (EC 3.1.3.9), and acetylesterase (EC 3.1.1.6). Sporofusarin was shown to exert a severe selective damage on lysosomal membranes. A demonstrable increase of lysosomal enzyme activity (especially arylsulphatases A and B and β-glucuronidase) in the supernatant occurred at minimum concentrations of sporofusarin. With increasing concentrations of the toxin, the release of lysosomal enzymes also rose at maximum concentration (1.6·10 −3 M) it amounted to 100% of the total activity for some enzymes. However, under the same experimental conditions the activity of mitochondrial and microsomal enzymes in the supernatant was 3.4–17.6% of the total activity. The role of the damaging effect of sporofusarin on lysosomal membranes in the pathogenesis of intoxication by this mycotoxin is discussed.

Spektrophotometrische Bestimmungsmethode für Serumcholinesterase(EC 3.1.1.8)-Varianten mit Succinylbischolin als Substrat

A simple and rapid method for the estimation of the hydrolysis of succinyl choline by serum cholinesterase variants is described. Succinyl choline, as substrate for the enzyme assay, has many advantages over other substrates (acetyl choline, benzoyl choline and butyryl choline) which have no clinical application. Choline, the hydrolytic product of succinyl choline, is oxidized to betaine aldehyde by choline oxidase (EC 1.1.99.1), a rat liver mitochondrial preparation; this is coupled to the reduction of cytochrome c which is measured at 550 nm. Fifty normal sera (UU), 17 heterozygous (UA) and 8 atypical (AA) were tested with this method, and on the basis of resistance to dibucaine (Cinchocain; Kalow, W. & Genest, K. (1957) Canad. J. Biochem. Physiol. 35, 339-346) inhibition, three distinct groups could be established using succinyl choline as substrate. These results are comparable with the standard optical method of Kalow & Genest (cf. above) using benzoyl choline as substrate.

Inhibition of yeast hydroxymethylglutaryl-CoA reductase by a rat liver mitochondrial preparation

FEBS LettersVolume 46, Issue 1-2 p. 20-22 Full-length articleFree Access Inhibition of yeast hydroxymethylglutaryl-CoA reductase by a rat liver mitochondrial preparation C. Madhosingh, C. Madhosingh Chemistry and Biology Research Institute 1Search for more papers by this authorB.B. Migicovsky, B.B. Migicovsky Chemistry and Biology Research Institute 1Search for more papers by this authorI.M. Wood, I.M. Wood Chemistry and Biology Research Institute 1Search for more papers by this author C. Madhosingh, C. Madhosingh Chemistry and Biology Research Institute 1Search for more papers by this authorB.B. Migicovsky, B.B. Migicovsky Chemistry and Biology Research Institute 1Search for more papers by this authorI.M. Wood, I.M. Wood Chemistry and Biology Research Institute 1Search for more papers by this author First published: September 15, 1974 https://doi.org/10.1016/0014-5793(74)80325-XCitations: 2 Contribution No. 766. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume46, Issue1-2September 15, 1974Pages 20-22 ReferencesRelatedInformation

Enzymatic Characteristics of CO‐Sensitive 26‐Hydroxylase System for 5β‐Cholestane‐3α, 7α, 12α‐triol in Rat‐Liver Mitochondria and Its Intramitochondrial Localization

The enxymatic characteristics of mitochondrial 26-hydroxylase system for 5β-cholestane-3α,7α,12α-triol were studied with rat liver mitochondria and the inner membrane-matrix fractions with special reference to its intramitochondrial localization. 1 Conditions for the assay of enzymatic activity of the hydroxylase system were established with rat liver mitochondrial preparations and inner membrane-matrix fractions derived by digitonin treatment. 2 It was established that rat liver mitochondria, as well as microsomes, possessed the hydroxylase system for 5β-cholestane-3α,7α,12α-triol as an intrinsic constituent. Product analyses revealed that only the mitochondrial hydroxylase system was specifically active for C-26 position. In contrast, the microsomal system was found to be apparently unspecific on C-26 position but rather more active for other adjacent positions. 3 Among the tested citric acid cycle intermediates and nicotinamide coenzymes, isocitrate and NADPH exerted the most remarkable enhancement of the 26-hydroxylase activity. NADP and NADH were totally inert under the present assay conditions. 4 Partial rupture of the mitochondrial structure by hypotonic or digitonin treatment was essential for the reactivity of 26-hydroxylase system under the present experimental conditions. Accessibility to the intramitochondrial reacting site of the exogenous reactants such as NADPH, isocitrate and 5β-cholestane-3α,7α,12α-triol in particular was apparently improved by the partial rupture. 5 The NADPH-dependent or isocitrate-dependent 26-hydroxylase system was totally insensitive to inhibitors of the respiratory electron transfer such as potassium cyanide, antimycin A, rotenone and amytal. However, it was specifically inhibited by phenyl isocyanide. 6 Remarkable sensitivity to carbon monoxide of the 26-hydroxylase system was demonstrated. Apparent Michaelis constant for oxygen and partition coefficient (between carbon monoxide and oxygen) of the 26-hydroxylase system were estimated to be approximately 10–20 μM and 0.1, respectively. Thus, the possible functioning of a “cytochrome P-450”-like entity in intramitochondrial 26-hydroxlase system was proposed. 7 The localization of 26-hydroxylase system was assigned to be in the inner membranematrix region, on the basis of the distribution of intramitochondrial marker enzymes during the course of serial solubilization by digitonin.

Aflatoxin inhibition of rat liver mitochondria

When aflatoxin B 1 (AFB 1) is added to an actively respiring rat liver mitochondrial preparation, 25–44% inhibition of electron transport is produced with concentrations ranging from 2.5–4.8 middot; 10 −4 M, respectively. The degree of inhibition levels off at 4.8 middot; 10 −4 M, which was shown to be in agreement with the critical micelle concentration. Submitochondrial or Gregg particles exhibit a maximum of 63% inhibition. Weanling rats maintained on a 5% casein semipurified diet for 15 days showed an approximate 30–50% reduction in the degree of aflatoxin inhibition for both mitochondria and Gregg particles compared to control animals fed a 20% casein diet ad libitum. The mitochondria of the protein-deprived animals had similar respiratory control ratios to normal animals. Dietary protein deficiency appears to exert its effect primarily at the site of action of aflatoxin rather than to alterations in membrane transport. The major site of inhibition of electron transport appeared to be between cytochromes b and c (c 1) as indicated by comparison of systems employing various substrates which donate their electrons to various portions of the electron transport system. At concentrations just below critical micelle formation, AFB 1 also reduced the ADP:O ratio, which was partially relieved by protein deficiency. The relevance of these findings to liver cell necrosis promoted by aflatoxin is discussed.

The influence of 1,1-bis(4'-(1"-carboxy-1"-methylpropoxy)-phenyl)cyclohexane (a new aryloxy compound, S-8527) on cholesterol metabolism in rats.

Abstract The effect of 1,1-bis[4′-(1′-carboxy-1′-methylpropoxy)-phenyl]cyclohexane (S-8527) on cholesterol metabolism and serum and liver lipids in rats has been studied. In some experiments S-8527 was compared to ethyl α- p -chlorophenoxyisobutyrate (Atromid-S, Clofibrate). When fed to rats for 3 weeks at a level of 0.03% of the diet, S-8527 did not affect weight gain but caused hepatomegaly. The extent of hepatomegaly (11% above control) was not as great as that seen with Atromid-S (42%). Serum cholesterol and triglyceride levels were significantly reduced, but liver lipid levels were not influenced. Cholesterol synthesis by liver slices from rats fed 0.3% of the drug for 3 weeks was reduced significantly ( P 14 C]acetate and P 14 C]cholesterol to 14 CO 2 by rat liver mitochondrial preparations was unaffected. One day after [4- 14 C]cholesterol was administered to rats fed S-8527 for 2 weeks significantly less [ 14 C]cholesterol was recoverable from the sera of treated rats ( P

Inhibition of RNA synthesis in mitochondria by daunomycin

Previous work has shown that daunomycin reacts with DNA of procaryotes and eucaryotes. Results with intact yeast cells indicate that mitochondria are preferentially inhibited by the drug at a concentration of about 10 μg/ml in most strains. Since the drug does not induce the petite mutation, at least over a period of one growth cycle, the replication of mitochondrial DNA is apparently unaffected. In a fermentable medium in the presence of the drug, cells develop only about 40 % of the respiratory activity of untreated cells. Incorporation of [ 14C]uracil into cells is depressed by the drug at low concentrations which inhibit growth of cells in a non-fermentable medium. In similar circumstances, incorporation of radioactive amino acid into proteins is unaffected in the short term. It was concluded that mitochondrial RNA synthesis was primarily affected by daunomycin. A preparation of rat liver mitochondria which incorporated [ 3H]UTP for at least 60 min, was inhibited about 30 % by addition of 10 μg/ml of the drug. Higher concentrations of the drug up to 20 μg/ml did not further depress the RNA synthesis. It was suggested that daunomycin inhibits the synthesis of a particular fraction of mitochondrial RNA.

The proton-translocating nicotinamide-adenine dinucleotide (phosphate) transhydrogenase of rat liver mitochondria.

1. The NAD(P) transhydrogenase activity of the soluble fraction of sonicated rat liver mitochondrial preparations was greater than the NAD-linked isocitrate dehydrogenase activity, and the NAD-linked and NADP-linked isocitrate dehydrogenase activities were not additive. The NAD-linked isocitrate dehydrogenase activity was destroyed by an endogenous autolytic system or by added nucleotide pyrophosphatase, and was restored by a catalytic amount of NADP. 2. We concluded that the isocitrate dehydrogenase of rat liver mitochondria was exclusively NADP-specific, and that the oxoglutarate/isocitrate couple could therefore be used unequivocally as redox reactant for NADP in experiments designed to operate only the NAD(P) transhydrogenase (or loop 0) segment of the respiratory chain in intact mitochondria. 3. During oxidation of isocitrate by acetoacetate in intact, anaerobic, mitochondria via the rhein-sensitive, but rotenone- and arsenite-insensitive, NAD(P) transhydrogenase, measurements of the rates of carbonyl cyanide p-trifluoromethoxyphenylhydrazone-sensitive and carbonyl cyanide p-trifluoromethoxyphenylhydrazone-insensitive pH change in the presence of various oxoglutarate/isocitrate concentration ratios gave an -->H(+)/2e(-) quotient of 1.94+/-0.12 for outward proton translocation by the NAD(P) transhydrogenase. 4. Measurements with a K(+)-sensitive electrode confirmed that the electrogenicity of the NAD(P) transhydrogenase reaction corresponded to the translocation of one positive charge per acid equivalent. 5. Sluggish reversal of the NAD(P) transhydrogenase reaction resulted in a significant inward proton translocation. 6. The possibility that isocitrate might normally be oxidized via loop 0 at a redox potential of -450mV, or even more negative, is discussed, and implies that a P/O quotient of 4 for isocitrate oxidation might be expected.

Effect of 2-acetoamidoethyl (p-chlorophenyl) (m-trifluoromethylphenoxy) acetate (halofenate) on cholesterol oxidation by rat liver mitochondria.

SummaryWe have compared the effects of halofenate [2-acetoamidoethyl (p-chlorophenyl) (m-trifluoromethylphenoxy) acetate] and clofibrate (ethyl p-chlorophenoxyisobutyrate) on rat serum and liver lipids and on oxidation of cholesterol by suitably fortified preparations of rat liver mitochondria. The halofenate was fed as 0.05% of the diet and the clofibrate as 0.3%. Both compounds caused increases in liver size and liver lipids. In the 3-week feeding experiment, both test compounds showed a significant hypocholesteremid effect.When complete incubation mixtures were used, the oxidation of 26-14C-cholesterol to 14CO2 was no different for liver mitochondrial preparations from halofenate, clofibrate, or control rats. However, in the absence of boiled supernatant factor (cytosol), oxidation of cholesterol was significantly higher with liver mitochondrial preparations from the drug-treated rats.

Inhibition of lysosomal enzyme release by catecholamines: Possible mediation by cyclic 3′, 5′-adenosine monophosphate

The catecholamines norepinephrine and epinephrine inhibit the release of enzymes from lysosomes obtained from a rat liver mitochondrial preparation. Cyclic 3′, 5′-adenosine monophosphate (cyclic AMP) elicits a similar action. Inhibitors of phosphodiesterase, such as theophylline and papaverine prevent enzyme release themselves and enhance the actions of added catecholamines and cyclic AMP. Propranolol, which prevents the activation of adenyl cyclase by catecholamines, reduces the effects of the latter but not the effect of cyclic AMP. Thus, it appears that inhibition of release of lysosomal enzymes by norepinephrine and epinephrine may be mediated by cyclic AMP.

Study of soluble lipoprotein in rat liver mitochondria.

1. A water-soluble lipoprotein was isolated and purified from osmotically shocked preparations of rat liver mitochondria by using a technique of Sephadex-sandwich disc electrophoresis. 2. The purified lipoprotein migrates as a distinct sharp zone in high-resolution electrophoretic systems, indicating high degree of purity. 3. The lipoprotein resembles mitochondrial membranes with respect to lipid composition and lipid/protein ratio. 4. The lipoprotein and its apoprotein fraction obtained by delipidization at -18 degrees C to -20 degrees C have common properties with respect to their fluorescence spectra, instability to storage and electrophoretic mobility. 5. The purified lipoprotein has an excitation maximum at 325nm and a fluorescence maximum at 418nm. 6. Storage at 4 degrees C for 4 days or repeated freezing and thawing results in 15-30% decrease in electrophoretic mobility. 7. The patterns of incorporation in vitro of [1-(14)C]leucine into proteins of the soluble lipoprotein and of mitochondrial membrane of isolated rat liver mitochondria suggest a probable precursor role for the apoprotein in the formation of mitochondrial membrane protein. 8. Lipoprotein preparations isolated from mitochondrial fractions of rat kidney, brain and heart and of chicken and mouse liver resemble closely that obtained from rat liver mitochondria, suggesting that the soluble lipoprotein could be a distinct entity of mitochondrial origin.