Search PubMed⌕ Search

Biomedical subjects

Y Stein

Publications and source records attributed to Y Stein.

At least 253 records · Page 14Linked to original sources
PubMed1969

Lecithin synthesis, intracellular transport, and secretion in rat liver. IV. A radioautographic and biochemical study of choline-deficient rats injected with choline-3H.

Injection of choline-(3)H into choline-deficient rats resulted in an enhanced incorporation of the label into liver lecithin, as compared to the incorporation of label into liver lecithin of normal rats. The results obtained with the use of different lecithin precursors indicate that in the intact liver cell, both in vivo and in vitro, exchange of choline with phosphatidyl-choline is not significant. The synthesis and secretion of lecithins by the choline-deficient liver compare favorably with the liver of choline-supplemented rats, when both are presented with labeled choline or lysolecithin as lecithin precursors. Radioautography of the choline-deficient liver shows that 5 min after injection of choline-(3)H the newly synthesized lecithin is found in the endoplasmic reticulum (62%), mitochondria (13%), and at the "cell boundary" (20%). The ratio of the specific activity of microsomal and mitochondrial lecithin, labeled with choline, glycerol, or linoleate, was 1.53 at 5 min after injection, but the ratio of the specific activity of phosphatidyl ethanolamine (PE), labeled with ethanolamine, was 5.3. These results indicate that lecithin and PE are synthesized mainly in the endoplasmic reticulum, and are transferred into mitochondria at different rates. The site of a precursor pool of bile lecithin was studied in the intact rat and in the perfused liver. Following labeling with choline-(3)H, microsomal lecithin isolated from perfused liver had a specific activity lower than that of bile lecithin, but the specific activity of microsomal linoleyl lecithin was comparable to that of bile lecithin between 30 and 90 min of perfusion. It is proposed that the site of the bile lecithin pool is located in the endoplasmic reticulum and that the pool consists mostly of linoleyl lecithin.

Amino Alcohols↗
PubMed1969

The metabolism of chylomicron cholesteryl ester in rat liver. A combined radioautographic-electron microscopic and biochemical study.

Chylomicrons containing labeled cholesterol, mainly (70%) present as cholesteryl ester, were injected intravenously into intact rats, and samples of liver were obtained 27-210 min later. Most (58-75%) of the injected label was recovered in the liver after 27-75 min. Hepatic uptake occurred without hydrolysis of the labeled cholesteryl ester. In separate experiments, in vitro perfusion of livers of similarly treated rats for 30-35 min washed out only 3-9% of the labeled sterol. Samples of liver and small intestine were prepared for electron microscopy with Aquon as the dehydrating agent. Good retention (70% or more) of labeled cholesterol and satisfactory preservation of ultrastructure were obtained. After 30 min, the radioautographic reaction was localized mainly over the region of the cell boundary of the parenchymal liver cells, with fewer grains being present over intracellular organelles. At later time intervals, when considerable hydrolysis of the labeled cholesteryl ester had occurred, the radioautographic reaction was more evenly distributed. Phagocytosed labeled lipid was seen in Kupffer cells after the larger lipid load; phagocytosis by parenchymal cells was not seen. In other experiments, cholesteryl ester hydrolase activity was found in all subcellular fractions, the microsome and plasma membrane fractions showing the highest activity per mg protein. The mechanism of cholesteryl ester transport into the liver cell may involve: (1) hydrolysis at the cell surface; or (2) slow entry of intact molecules followed by intracellular hydrolysis of the ester bond.

Animals↗
PubMed1969

Phospholipases in arterial tissue. IV. The role of phosphatide acyl hydrolase, lysophosphatide acyl hydrolase, and sphingomyelin choline phosphohydrolase in the regulation of phospholipid composition in the normal human aorta with age.

The role of phospholipases in the regulation of the changing phospholipid composition of normal human aortae with age was studied. Portions of grossly and histologically lesion-free ascending aortae from 16 females and 29 males obtained at autopsy, were analyzed for deoxyribonucleic acid (DNA), phospholipid, and cholesterol content and phospholipid composition. Enzymic activity toward four substrates, lecithin (LE), phosphatidyl ethanolamine, lysolecithin, and sphingomyelin (SP), was determined on portions of the same homogenate. By regression analysis for correlation between all determinations and age the following results were obtained: (a) total phospholipids and choleserol increased linearly with age; (b) the increase in sphingomyelin accounted for about 70% of the phospholipid increment; (c) hydrolysis of lecithin and phosphatidyl ethanolamine increased markedly with age, that of lysolecithin only moderately; (d) hydrolysis of sphingomyelin decreased with age; and (e) an inverse relation between the SP/LE ratio and age and sphingomyelinase/lecithinase activity and age was obtained. These results were interpreted to indicate that a causal relation exists between the fall in sphingomyelinase activity, both absolute and relative to lecithinase activity, and the accumulation of sphingomyelin with age.

Adolescent↗
PubMed1968

Acylation of lysophosphatides by plasma membrane fractions of rat liver.

The plasma membrane fraction of rat liver was isolated and incubated with labeled lysophosphatides in the presence of cofactors; the acylation of lysolecithin to lecithin by the fraction was compared to that of the rough and smooth microsomes. The purity of the isolated fractions was ascertained by enzyme markers and electron microscopy, and the maximal contamination of the plasma membrane fraction by microsomes did not exceed 20%. Under conditions at which the reaction was proportional to the amount of enzyme used, the plasma membrane had a specific activity similar to that of the smooth and rough microsomes. With doubly labeled lysolecithin (containing palmitic acid-(14)C and choline-(3)H) it was shown that the lecithin formed retained the same ratio of the two labels, which indicated that lysolecithin was converted to lecithin through an acylation reaction. The newly formed lecithin was shown to be bound to the plasma membrane fraction; this suggested that it is incorporated into the structure of the membrane itself.

Acetates↗