scholarly journals Incorporation of oxygen-18 into the 25-position of cholecalciferol by hepatic cholecalciferol 25-hydroxylase

1978 ◽  
Vol 175 (2) ◽  
pp. 479-482 ◽  
Author(s):  
T C Madhok ◽  
H K Schnoes ◽  
H F DeLuca
Keyword(s):  
Rat Liver ◽  
Mitochondrial Fraction ◽  
The Other ◽  
Mixed Function Oxidase ◽  
25 Hydroxycholecalciferol

The oxygen enzymically inserted as a hydroxy function by rat liver post-mitochondrial fraction into the 25-position of cholecalciferol to giver 25-hydroxycholecaliferol is derived exclusively from molecular O2. Therefore like the other two cholecalciferol hydroxylases, i.e. 25-hydroxycholecalciferol 1alpha-hydroxylase and 25-hydroxycholecalciferol 24-hydroxylase, the cholecalciferol 25-hydroxylase is also a mono-oxygenase (‘mixed-function oxidase’).

scholarly journals STUDY OF MITOCHONDRIA IN RAT LIVER

1962 ◽  
Vol 15 (3) ◽  
pp. 489-501 ◽  
Author(s):  
Gunter F. Bahr ◽  
Elmar Zeitler
Keyword(s):  
Electron Microscopy ◽  
Rat Liver ◽  
Linear Growth ◽  
Mitochondrial Fraction ◽  
The Other ◽  
Quantitative Electron Microscopy ◽  
Normal Rat ◽  
Log Normal ◽  
Log Normal Distribution ◽  
Particle Weight

The electron microscope has been used to determine the weight distribution of isolated subcellular particles from normal rat liver. The following results are reported: (1) There exist at least two well defined weight populations of subcellular particles; their respective median weights are 1.3 x 10-14 and 11 x 10-14 gm. The lighter fraction is considered to consist of lysosomes, the heavier of mitochondria. (2) The mitochondrial fraction shows a log-normal distribution of the particle weight. (3) By the introduction of morphologic criteria, the mitochondrial fraction is divided into two groups, one consisting of a spherical, the other of an oblong type of particle. The data found support the following concepts: (a) Mitochondria increase their weight from a certain size up by linear growth. (b) Mitochondria divide. The division is not necessarily symmetric; in all cases, however, one part of the division product is a spherical particle. It is felt that these results constitute a valuable demonstration of the general capabilities of quantitative electron microscopy and may stimulate many other useful applications of this technique in cytology, bacteriology, and virology.

scholarly journals Comparative studies on the 25-hydroxylations of cholecalciferol and 1α-hydroxycholecalciferol in perfused rat liver

1978 ◽  
Vol 170 (3) ◽  
pp. 495-502 ◽  
Author(s):  
Masafumi Fukushima ◽  
Yasuho Nishii ◽  
Michiko Suzuki ◽  
Tatsuo Suda
Keyword(s):  
Vitamin D ◽  
Rat Liver ◽  
Linear Relation ◽  
Comparative Studies ◽  
Similar Rate ◽  
The Other ◽  
Perfused Rat Liver ◽  
Km Value ◽  
Derivatives Of ◽  
25 Hydroxycholecalciferol

The 25-hydroxylations of [3H]cholecalciferol and 1α-hydroxy[3H]cholecalciferol in perfused rat liver were compared. Results showed that about twice as much 1α(OH)D3 (1α-hydroxycholecalciferol) was incorporated into the liver as cholecalciferol. 25-Hydroxy[3H]cholecalciferol and 1α-25-dihydroxy[3H]cholecalciferol were not incorporated significantly. Livers isolated from vitamin D-deficient rats formed the 25-hydroxy derivatives of cholecalciferol and 1α(OH)D3 respectively linearly with time for at least 120min. The rate of 1α,25(OH)2D3 (1α,25-dihydroxycholecalciferol) production increased exactly 10-fold on successive 10-fold increases in the dose of 1α(OH)D3, suggesting that hepatic 25-hydroxylation of 1α(OH)D3 is not under metabolic control. On the other hand, the rate of conversion of cholecalciferol into 25(OH)D3 (25-hydroxycholecalciferol) did not increase linearly with increase in the amount of cholecalciferol in the perfusate. The 25-hydroxylation of cholecalciferol seemed to proceed at a similar rate to that of 1α(OH)D3 at doses of less than 1nmol, but with doses of more than 2.5nmol, the conversion of cholecalciferol into 25(OH)D3 became much less efficient, though the linear relation between the amounts of substrate and product was maintained. A reciprocal plot of data on the 25-hydroxylation of cholecalciferol gave two Km values of about 5.6nm and 1.0μm, whereas that for the 25-hydroxylation of 1α(OH)D3 gave a single Km value of about 2.0μm. These results suggest that there are two modes of 25-hydroxylation of cholecalciferol in the liver, which seem to be closely related to the mechanism of control of 25(OH)D3 production by the liver.

scholarly journals The fractionation of nuclei from mammalian cells by zonal centrifugation

1968 ◽  
Vol 109 (1) ◽  
pp. 127-135 ◽  
Author(s):  
I R Johnston ◽  
A P Mathias ◽  
F. Pennington ◽  
D. Ridge
Keyword(s):  
Rat Liver ◽  
Mammalian Cells ◽  
Mouse Liver ◽  
The Other ◽  
Slow Speed ◽  
Adult Rats ◽  
Sucrose Solutions ◽  
Liver Nuclei ◽  
Effect Of Age ◽  
Zonal Rotor

1. Purified liver nuclei from adult rats separate into two main zones when centrifuged in the slow-speed zonal rotor. One zone contains diploid nuclei, the other tetraploid. 2. The effect of age on the pattern of rat liver ploidy was examined. Tetraploid nuclei are virtually absent from young animals. They increase in proportion steadily with age. Partial hepatectomy disturbs the pattern of ploidy. 3. The zonal centrifuge permits the separation of diploid, tetraploid, octaploid and hexadecaploid nuclei from mouse liver. 4. Rat liver nuclei are isopycnic with sucrose solutions of density 1·35 at 5°.

scholarly journals Ganglioside incorporation and release by the isolated perfused rat liver

1991 ◽  
Vol 274 (2) ◽  
pp. 581-585 ◽  
Author(s):  
S C Kivatinitz ◽  
A Miglio ◽  
R Ghidoni
Keyword(s):  
Rat Liver ◽  
The Other ◽  
Regulatory Role ◽  
Isolated Perfused Rat Liver ◽  
Order Kinetic ◽  
Perfused Rat Liver ◽  
Ganglioside Gm1 ◽  
First Order ◽  
Pseudo First Order

The fate of exogenous ganglioside GM1 labelled in the sphingosine moiety, [Sph-3H]GM1, administered as a pulse, in the isolated perfused rat liver was investigated. When a non-recirculating protocol was employed, the amount of radioactivity in the liver and perfusates was found to be dependent on the presence of BSA in the perfusion liquid and on the time elapsed after the administration of the ganglioside. When BSA was added to the perfusion liquid, less radioactivity was found in the liver and more in the perfusate at each time tested, for up to 1 h. The recovery of radioactivity in the perfusates followed a complex course which can be described by three pseudo-first-order kinetic constants. The constants, in order of decreasing velocity, are interpreted as: (a) the dilution of the labelled GM1 by the constant influx of perfusion liquid; (b) the washing off of GM1 loosely bound to the surface of liver cells; (c) the release of gangliosides from the liver. Process (b) was found to be faster in the presence of BSA, probably owing to the ability of BSA to bind gangliosides. The [Sph-3H]GM1 in the liver underwent metabolism, leading to the appearance of products of anabolic (GD1a, GD1b) and catabolic (GM2, GM3) origin; GD1a appeared before GM2 and GM3 but, at times longer than 10 min, GM2 and GM3 showed more radioactivity than GD1a. At a given time the distribution of the radioactivity in the perfusates was quite different from that of the liver. In fact, after 60 min GD1a was the only metabolite present in any amount, the other being GM3, the quantity of which was small. This indicates that the liver is able to release newly synthesized gangliosides quite specifically. When a recirculating protocol was used, there were more catabolites and less GD1a than with the non-recirculating protocol. A possible regulatory role of ganglioside re-internalization on their own metabolism in the liver is postulated.

FURTHER STUDIES ON THE BINDING OF γ-AMINOBUTYRIC ACID BY BRAIN

1967 ◽  
Vol 45 (12) ◽  
pp. 1795-1807 ◽  
Author(s):  
Paula Strasberg ◽  
K. A. C. Elliott
Keyword(s):  
Rat Brain ◽  
Mitochondrial Fraction ◽  
Sodium Ion ◽  
The Other ◽  
Aminobutyric Acid ◽  
Sodium Ions ◽  
Ninhydrin Reaction ◽  
Gaba Content

Factors which can interfere with the paper chromatographic – ninhydrin method for determining γ-aminobutyric acid (GABA) are described. The GABA–ninhydrin reaction does not involve loss of CO2. GABA that is occluded in subcellular particles in plain sucrose homogenates of rat brain does not readily exchange with radioactive GABA in solution. The relevant particles are found mostly in the "mitochondrial fraction". These particles deteriorate with time and manipulations, and tend to lose much of their GABA content. The presence of sodium (but not of potassium, calcium, or magnesium) in the suspending medium allows considerably more GABA to be bound. The extra bound GABA is exchangeable with free labelled GABA. Sodium also promotes some exchange between free and occluded GABA. It is concluded from the present and previous results that in brain in vivo very little GABA exists in a freely diffusing situation. There are two forms of bound GABA. One of these is an occluded or storage form which does not readily exchange with free GABA though exchange is to some extent promoted by sodium ions. The other is a form which occurs only in the presence of sodium ion and is freely exchangeable with GABA in solution.

Mixed Function Oxidase and Ethanol Metabolism in Perfused Rat Liver

Science ◽  
1972 ◽  
Vol 176 (4042) ◽  
pp. 1435-1437 ◽  
Author(s):  
I. E. Hassinen ◽  
R. H. Ylikahri
Keyword(s):  
Rat Liver ◽  
Ethanol Metabolism ◽  
Mixed Function Oxidase ◽  
Perfused Rat Liver

scholarly journals Subcellular distribution and characteristics of trihydroxycoprostanoyl-CoA synthetase in rat liver

1989 ◽  
Vol 257 (1) ◽  
pp. 221-229 ◽  
Author(s):  
L Schepers ◽  
M Casteels ◽  
K Verheyden ◽  
G Parmentier ◽  
S Asselberghs ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cholic Acid ◽  
Rat Liver ◽  
Subcellular Distribution ◽  
The Other ◽  
Acid Activation ◽  
Long Chain Fatty Acids ◽  
Microsomal Membranes ◽  
Triton X ◽  
Long Chain

The subcellular distribution and characteristics of trihydroxycoprostanoyl-CoA synthetase were studied in rat liver and were compared with those of palmitoyl-CoA synthetase and choloyl-CoA synthetase. Trihydroxycoprostanoyl-CoA synthetase and choloyl-CoA synthetase were localized almost completely in the endoplasmic reticulum. A quantitatively insignificant part of trihydroxycoprostanoyl-CoA synthetase was perhaps present in mitochondria. Peroxisomes, which convert trihydroxycoprostanoyl-CoA into choloyl-CoA, were devoid of trihydroxycoprostanoyl-CoA synthetase. As already known, palmitoyl-CoA synthetase was distributed among mitochondria, peroxisomes and endoplasmic reticulum. Substrate- and cofactor- (ATP, CoASH) dependence of the three synthesis activities were also studied. Cholic acid and trihydroxycoprostanic acid did not inhibit palmitoyl-CoA synthetase; palmitate inhibited the other synthetases non-competitively. Likewise, cholic acid inhibited trihydroxycoprostanic acid activation non-competitively and vice versa. The pH curves of the synthetases did not coincide. Triton X-100 affected the activity of each of the synthetases differently. Trihydroxycoprostanoyl-CoA synthetase was less sensitive towards inhibition by pyrophosphate than choloyl-CoA synthetase. The synthetases could not be solubilized from microsomal membranes by treatment with 1 M-NaCl, but could be solubilized with Triton X-100 or Triton X-100 plus NaCl. The detergent-solubilized trihydroxycoprostanoyl-CoA synthetase could be separated from the solubilized choloyl-CoA synthetase and palmitoyl-CoA synthetase by affinity chromatograpy on Sepharose to which trihydroxycoprostanic acid was bound. Choloyl-CoA synthetase and trihydroxycoprostanoyl-CoA synthetase could not be detected in homogenates from kidney or intestinal mucosa. The results indicate that long-chain fatty acids, cholic acid and trihydroxycoprostanic acid are activated by three separate enzymes.

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