Study of soluble lipoprotein in rat liver mitochondria

Abstract

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.

Regulation of Fructose‐Bisphosphatase Activity

“…This observation has been further studied and it has been reported that incubation with ATP or ADP causes an inactivation of rabbit liver Fru-P,ase that develops slowly and can be reversed or prevented by a number of chelating agents, such as 3-P-glycerate, EDTA, pyrophosphate, citrate, oxaloacetate, phosphate Taketa et al, 1971), and oleate (Carlson et al, 1973). This observation has been confirmed by a number of other workers who have reported that swine kidney Fru-P,ase (Mendicino et al, 1966;Kratowich and Mendicino, 1970) and rabbit muscle Fru-P,ase (Fu and Kemp, 1973) are inactivated by ADP and ATP. It has been suggested that the reversal of the ADP and ATP inactivation by 3-P-glycerate may contribute to regulation of the activity of the enzyme Taketa et al, 1971).…”

Involvement of binding lipoproteins in the absorption and transport of α-tocopherol in the rat

“…After an initial centrifugation at 100OOg for lOmin to sediment cell debris, mucus and mitochondria, the supernatant was spun at 105000g for 60min to obtain clear cytosol. This was concentrated by reverse dialysis against Polywax (polyethylene glycol) 6000 (Koppikar et al, 1971).…”

“…A column (1.8cmx 50cm) uniformly packed with Sephadex G-200 gel and equilibrated with 0.05M-sodium phosphate buffer (pH7.4) was employed for the isolation and initial purification of a-tocopherol-binding protein. A sample of cytosol or serum containing 70-100mg of protein was loaded on the gel and elution carried out in the cold (4°C) at a flow rate of 20ml/h with the phosphate buffer mentioned above, and fractions (2.5ml) were collected (Koppikar et al, 1971). Extinction of the various fractions was measured in a Shimadzu QV 50 spectrophotometer at 280nm in a 1cm light-path cell.…”

“…Polyacrylamide-gel electrophoresis was carried out in a 3.5 % running gel. The spacer gel of 2.5 % polyacrylamide, as modified by Koppikar et al (1971), was used. All other details of the electrophoretic system wereessentiallyas described byNarayan etal.…”

Lipophilic Proteins of Mitochondria from Microaerobic and Aerobic Continuous Cultures of Saccharomyces cerevisiae

“…of both the cytoplasmic and mitochondrial protein-synthesizing systems are required for the assembly of some complexes of the inner membrane of yeast mitochondria, e.g., cytochrome c oxidase (4,10,20) and adenosine triphosphatase (18,20). A significant proportion of the mitochondrial protein products can be extracted selectively from rat liver (1,(6)(7)(8)(9) and yeast (13,19) mitochondria with organic solvents. Kadenbach and Hadvary (7), Sierra and Tzagoloff (17), and Michel and Neupert (12) have discussed the possible role of small lipophilic molecules in the synthesis and assembly of mitochondrial membranes.…”