scholarly journals Evidence for the reversibility of the acyl-CoA:lysophosphatidylcholine acyltransferase in microsomal preparations from developing safflower (Carthamus tinctorius L.) cotyledons and rat liver

1984 ◽  
Vol 223 (2) ◽  
pp. 305-314 ◽  
Author(s):  
S Stymne ◽  
A K Stobart
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Rat Liver ◽  
Bovine Serum ◽  
Exchange Process ◽  
High Specificity ◽  
Carthamus Tinctorius ◽  
Back Reaction ◽  
Acyl Exchange ◽  
Rate Limiting Step

Acyl exchange between acyl-CoA and position 2 of sn-phosphatidylcholine occurs in the microsomal preparations of developing safflower cotyledons. Evidence is presented to show that the acyl exchange is catalysed by the combined back and forward reactions of an acyl-CoA:lysophosphatidylcholine acyltransferase (EC 2.3.1.23). The back reaction of the enzyme was demonstrated by the stimulation of the acyl exchange with free CoA and by the observation that the added CoA was acylated with acyl groups from position 2 of sn-phosphatidylcholine. Re-acylation of the, endogenously produced, lysophosphatidylcholine with added acyl-CoA occurred with the same specificity as that observed with added palmitoyl lysophosphatidylcholine. A similar acyl exchange, catalysed by an acyl-CoA:lysophosphatidylcholine acyltransferase, occurred in microsomal preparations of rat liver. The enzyme from safflower had a high specificity for oleate and linoleate, whereas arachidonate was the preferred acyl group in the rat liver microsomal preparations. The rate of the back reaction was 3-5% and 0.2-0.4% of the forward reaction in the microsomal preparations of safflower and rat liver respectively. Previous observations, that the acyl exchange in safflower microsomal preparations was stimulated by bovine serum albumin and sn-glycerol 3-phosphate, can now be explained by the lowered acyl-CoA concentrations in the incubation mixture with albumin and in the increase in free CoA in the presence of sn-glycerol 3-phosphate (by rapid acylation of sn-glycerol 3-phosphate with acyl groups from acyl-CoA to yield phosphatidic acid). Bovine serum albumin and sn-glycerol 3-phosphate, therefore, shift the equilibrium in acyl-CoA:lysophosphatidylcholine acyltransferase-catalysed reactions towards the rate-limiting step in the acyl exchange process, namely the removal of acyl groups from phosphatidylcholine. The possible role of the acyl exchange in the transfer of acyl groups between complex lipids is discussed.

scholarly journals A modified radioimmunoassay of aldosterone

1995 ◽  
Vol 41 (2) ◽  
pp. 33-34
Author(s):  
N. P. Goncharov ◽  
G. V. Katsiya ◽  
V. Yu. Butnev ◽  
L. B. Khagundokova
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Adrenal Cortex ◽  
Bovine Serum ◽  
High Specificity ◽  
New Method ◽  
Isolation And Purification ◽  
Cross Reactions ◽  
Chromatographic Isolation

A method of radioimmunoassay of aldosterone in the blood of humans and monkeys has been developed. Antiserum was prepared on rabbits against aldosterone-3-(0-carboxymethyloxime) conjugate with bovine serum albumin. The specificity of antiserum was tested in cross-reactions with 32 related steroids. High specificity of the antiserum in this method helped measure aldosterone levels without preliminary chromatographic isolation and purification of this compound. The sensitivity of the new method is 12.5 pg per 0.1 ml. Reproducibility of the method between different series of measurements was no more than 15%, within the same series below 12%. The method was used to assess the mineralocorticoid function of the adrenal cortex of man and monkeys.

scholarly journals The comparative specificity of three oestradiol-binding proteins. Rat α-foetoprotein, rat liver 17β-hydroxy steroid dehydrogenase and anti-(oestradiol-6-carboxymethyloxime-bovine serum albumin) antiserum

1975 ◽  
Vol 151 (3) ◽  
pp. 513-518 ◽  
Author(s):  
C Laurant ◽  
S D de Lauzon ◽  
N Cittanova ◽  
E Nunez ◽  
M F Jayle
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Rat Liver ◽  
Bovine Serum ◽  
Binding Proteins ◽  
Specific Binding ◽  
Naturally Occurring ◽  
Γ Globulins ◽  
Hydroxy Steroid ◽  
Steroid Dehydrogenase

1. The specificity of 3 oestradiol-binding proteins was studied. Two of these proteins are naturally occurring (rat α-foetoprotein and rat liver microsomal 17β-hydroxy steroid dehydrogenase) and the third is an artificially induced model, anti-(oestradiol-6-carboxymethyloxime-bovine serum albumin) γ-globulins. 2. A specific binding procedure for each protein model permitted a determination of its affinity for oestradiol and for 30 other steroids. 3. The results obtained have brought to light the different areas of the steroid molecule that are important for its recognition by each of the three proteins. The two naturally occurring proteins (α-foetoprotein and 17β-hydroxy steroid dehydrogenase) recognize the edge of the steroid defined by C-4, C-6, C-8 and C-15. On the other hand, the γ-globulins recognize the opposite edge, i.e. that defined by C-2, C-10, C-11 and C-17. 4. Diethylstilboestrol, whose structure is analogous to that of a steroid, is only recognized by the two naturally occurring proteins.

scholarly journals Serum albumin enhances the uptake of [3H]cholesterol from phosphatidylcholine vesicles by cultured human fibroblasts

1984 ◽  
Vol 220 (2) ◽  
pp. 605-608 ◽  
Author(s):  
J P Slotte ◽  
S Björkerud
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Bovine Serum ◽  
Human Lung ◽  
Exchange Process ◽  
Human Fibroblasts ◽  
Lung Fibroblasts ◽  
Molar Ratio ◽  
Human Lung Fibroblasts ◽  
Cultured Human Fibroblasts

Cultured human lung fibroblasts, incubated with cholesterol/phosphatidylcholine vesicles (cholesterol: phosphatidylcholine molar ratio 1:1) incorporated vesicle [3H]-cholesterol linearly for at least 48 h by an exchange process without gaining sterol mass. The incorporation of [3H]cholesterol by the cells was markedly enhanced in the presence of purified bovine serum albumin. A fraction of the incorporated vesicle [3H]cholesterol was esterified by the cells.

scholarly journals Rat liver microsomes catalyse mannosyl transfer from GDP-d-mannose to retinyl phosphate with high efficiency in the absence of detergents

1981 ◽  
Vol 200 (3) ◽  
pp. 529-538 ◽  
Author(s):  
Yoshihiro Shidoji ◽  
Luigi M. De Luca
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Rat Liver ◽  
Bovine Serum ◽  
High Efficiency ◽  
Liver Microsomes ◽  
Water Soluble ◽  
Rat Liver Microsomes ◽  
Uptake System ◽  
Dolichyl Phosphate

In the absence of detergent, the transfer of mannose from GDP-mannose to rat liver microsomal vesicles was highly stimulated by exogenous retinyl phosphate in incubations containing bovine serum albumin, as measured in a filter binding assay. Under these conditions 65% of mannose 6-phosphatase activity was latent. The transfer process was linear with time up to 5min and with protein concentration up to 1.5mg/0.2ml. It was also temperature-dependent. The microsomal uptake of mannose was highly dependent on retinyl phosphate and was saturable against increasing amounts of retinyl phosphate, a concentration of 15μm giving half-maximal transfer. The uptake system was also saturated by increasing concentrations of GDP-mannose, with an apparent Km of 18μm. Neither exogenous dolichyl phosphate nor non-phosphorylated retinoids were active in this process in the absence of detergent. Phosphatidylethanolamine and synthetic dipalmitoylglycerophosphocholine were also without activity. Several water-soluble organic phosphates (1.5mm), such as phenyl phosphate, 4-nitrophenyl phosphate, phosphoserine and phosphocholine, did not inhibit the retinyl phosphate-stimulated mannosyl transfer to microsomes. This mannosyl-transfer activity was highest in microsomes and marginal in mitochondria, plasma and nuclear membranes. It was specific for mannose residues from GDP-mannose and did not occur with UDP-[3H]galactose, UDP- or GDP-[14C]glucose, UDP-N-acetyl[14C]-glucosamine and UDP-N-acetyl[14C]galactosamine, all at 24μm. The mannosyl transfer was inhibited 85% by 3mm-EDTA and 93% by 0.8mm-amphomycin. At 2min, 90% of the radioactivity retained on the filter could be extracted with chloroform/methanol (2:1, v/v) and mainly co-migrated with retinyl phosphate mannose by t.l.c. This mannolipid was shown to bind to immunoglobulin G fraction of anti-(vitamin A) serum and was displaced by a large excess of retinoic acid, thus confirming the presence of the β-ionone ring in the mannolipid. The amount of retinyl phosphate mannose formed in the bovine serum albumin/retinyl phosphate incubation is about 100-fold greater than in incubations containing 0.5% Triton X-100. In contrast with the lack of activity as a mannosyl acceptor for exogenous dolichyl phosphate in the present assay system, endogenous dolichyl phosphate clearly functions as an acceptor. Moreover in the same incubations a mannolipid with chromatographic properties of retinyl phosphate mannose was also synthesized from endogenous lipid acceptor. The biosynthesis of this mannolipid (retinyl phosphate mannose) was optimal at MnCl2 concentrations between 5 and 10mm and could not be detected below 0.6mm-MnCl2, when synthesis of dolichyl phosphate mannose from endogenous dolichyl phosphate was about 80% of optimal synthesis. Under optimal conditions (5mm-MnCl2) endogenous retinyl phosphate mannose represented about 20% of dolichyl phosphate mannose at 15min of incubation at 37°C.

scholarly journals Properties of rat liver microsomal stearoyl-coenzyme A desaturase

1977 ◽  
Vol 161 (2) ◽  
pp. 431-437 ◽  
Author(s):  
R Jeffcoat ◽  
P R Brawn ◽  
R Safford ◽  
A T James
Keyword(s):  
Bovine Serum Albumin ◽  
Serum Albumin ◽  
Rat Liver ◽  
Bovine Serum ◽  
Desaturase Activity ◽  
Cytochrome B5 ◽  
Fatty Acyl ◽  
Enzyme Preparations ◽  
Stearoyl Coa Desaturase ◽  
Nadh Cytochrome

1. Rat liver microsomal stearoyl-CoA desaturase activity was shown to be stimulated by both bovine serum albumin and a basic cytoplasmic protein from rat liver. 2. Partially purified desaturase is unaffected by either of these two proteins. 3. Bovine serum albumin appears to exert its effect on the crude system by protecting the desaturase substrate, stearoly-CoA, from the action of endogenous thiolesterases. 4. By using partially purified enzyme preparations, it was possible to establish the substate specificity of the delta9-fatty acyl-CoA desaturase with the C14, C15, C16, C17, C18 and C19 fatty acyl-CoA substrates. Maximum enzyme activity was shown with stearoyl-CoA decreasing with both palmitoyl-CoA and nonadecanoyl-CoA, as reported previously for free fatty acids. 5. Both cytochrome b5 and NADH-cytochrome b5 reductase (EC 1.6.2.2) are required for these studies and a method is described for the purification of homogeneous preparations of detergent-isolated cytochrome b5 from rat liver. 6. From amino acid analyses, a comparison was made of the hydrophobicity of the membrane portion of cytochrome b5 with the hydrophobicity reported for stearoyl-CoA desaturase. The close resemblance of the two values suggested that unlike cytochrome b5 and its reductase, the stearoyl-CoA desaturase may be largely buried in the endoplasmic reticulum.

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