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J L Goldstein

Publications and source records attributed to J L Goldstein.

At least 19 recordsLinked to original sources
PubMed1979

Optimum probabilistic processing in colour perception. I. Colour discrimination.

A comprehensive account of wavelength discrimination and colour saturation discrimination is given in terms of optimum probabilistic signal detection. The theory is a logical deduction from statistical estimation theory of the visual estimate of the spectral parameters of the stimulus. In place of geometrical concepts associated with colour-space geometry, stimulus discriminability is determined by optimum decision rules given by likelihood ratio tests on statistics that are postulated for the trichromatic responses. The classical line element theory and its formulations are deduced to be discriminability measures between signals. The different mathematical forms of classical theory are shown to correspond to different statistical constraints.

Color Perception↗
PubMed1979

Optimum probabilistic processing in colour perception. II. Colour vision as template matching.

A statistical approach to account for psychophysical phenomena in human colour vision is presented. The central visual processor is viewed as an optimum recognizer of stochastic patterns supplied by the periphery. The processor makes an optimum estimate of the spectral parameters of the stimulus, given the wavelength filter characteristics of the periphery, the stochastic nature of the information and an internal template to which the external stimulus is matched. The estimate is constrained in ways inferred from empirical phenomena. Subjective brightness of monochromatic stimuli and related constant brightness manifolds in the colour space constitute the constraint for brightness estimation. Results analogous and in accord with those of earlier line element theories are obtained. The Bezold-Brücke hue shift constitutes the basic constraint for hue estimation. The hue estimate involves interrelation between the fields in the experiment. Similarities and differences both in basic conceptions and results introduced by the template matching notions are discussed.

Color Perception↗
PubMed1979

Coated pits, coated vesicles, and receptor-mediated endocytosis.

Proteins and peptides can enter cells by receptor-mediated endocytosis, a coupled process by which selected extracellular proteins or peptides are first bound to specific cell surface receptors and then rapidly internalised by the cell. Internalisation follows clustering of the receptors in specialised regions of the cell surface called coated pits that invaginate to form intracellular coated vesicles. It is now recognised that receptor-mediated endocytosis has a fundamental role in the growth, nutrition and differentiation of animal cells.

Animals↗
PubMed1979

Reconstituted low density lipoprotein: a vehicle for the delivery of hydrophobic fluorescent probes to cells.

Previous studies have shown that the cholesteryl ester core of plasma low density lipoprotein (LDL) can be extracted with heptane and replaced with a variety of hydrophobic molecules. In the present report we use this reconstitution technique to incorporate two fluorescent probes, 3-pyrenemethyl-23, 24-dinor-5-cholen-22-oate-3 beta-yl oleate (PMCA oleate) and dioleyl fluorescein, into heptane-extracted LDL. Both fluorescent lipoprotein preparations were shown to be useful probes for visualizing the receptor-mediated endocytosis of LDL in cultured human fibroblasts. When normal fibroblasts were incubated at 37 degrees C with either of the fluorescent LDL preparations, fluorescent granules accumulated in the perinuclear region of the cell. In contrast, fibroblasts from patients with the homozygous form of familial hypercholesterolemia (FH) that lack functional LDL receptors did not accumulate visible fluorescent granules when incubated with the fluorescent reconstituted LDL. A fluorescence-activated cell sorter was used to quantify the fluorescence intensity of individual cells that had been incubated with LDL reconstituted with dioleyl fluorescein. With this technique a population of normal fibroblasts could be distinguished from a population of FH fibroblasts. The current studies demonstrate the feasibility of using fluorescent reconstituted LDL in conjunction with the cell sorter to isolate mutant cells lacking functional LDL receptors.

Cells, Cultured↗
PubMed1979

Binding site on macrophages that mediates uptake and degradation of acetylated low density lipoprotein, producing massive cholesterol deposition.

Resident mouse peritoneal macrophages were shown to take up and degrade acetylated (125)I-labeled low density lipoprotein ((125)I-acetyl-LDL) in vitro at rates that were 20-fold greater than those for the uptake and degradation of (125)I-LDL. The uptake of (125)I-acetyl-LDL and its subsequent degradation in lysosomes were attributable to a high-affinity, trypsin-sensitive, surface binding site that recognized acetyl-LDL but not native LDL. When (125)I-acetyl-LDL was bound to this site at 4 degrees C and the macrophages were subsequently warmed to 37 degrees C, 75% of the cell-bound radioactivity was degraded to mono[(125)I]iodotyrosine within 1 hr. The macrophage binding site also recognized maleylated LDL, maleylated albumin, and two sulfated polysaccharides (fucoidin and dextran sulfate) indicating that negative charges were important in the binding reaction. A similar binding site was present on rat peritoneal macrophages, guinea pig Kupffer cells, and cultured human monocytes but not on human lymphocytes or fibroblasts, mouse L cells or Y-1 adrenal cells, or Chinese hamster ovary cells. Uptake and degradation of acetyl-LDL via this binding site stimulated cholesterol esterification 100-fold and produced a 38-fold increase in the cellular content of cholesterol in mouse peritoneal macrophages. Although the physiologic significance, if any, of this macrophage uptake mechanism is not yet known, we hypothesize that it may mediate the degradation of denatured LDL in the body and thus serve as a "backup" mechanism for the previously described receptor-mediated degradation of native LDL that occurs in parenchymal cells. Such a scavenger pathway might account for the widespread deposition of LDL-derived cholesteryl esters in macrophages of patients with familial hypercholesterolemia in whom the parenchymal cell pathway for LDL degradation is blocked, owing to a genetic deficiency of receptors for native LDL.

Acetylation↗
PubMed1979

Squalene synthetase activity in human fibroblasts: regulation via the low density lipoprotein receptor.

Squalene synthetase (farnesyltransferase; farnesyl diphosphate:farnesyl-diphosphate farnesyltransferase, EC 2.5.1.21), the enzyme in the cholesterol biosynthetic pathway that converts farnesyl pyrophosphate into squalene, is subject to regulation in cultured human fibroblasts. When cholesterol-carrying low density lipoprotein (LDL) was removed from the serum of the culture medium, squalene synthetase activity increased 8-fold over 24 hr. When LDL was added back to the medium, squalene synthetase was slowly suppressed, 50% and 90% reduction occurring in 15 and 48 hr, respectively. Suppression of squalene synthetase required uptake of LDL via the LDL receptor; hence, it did not occur in mutant fibroblasts from a patient with homozygous familial hypercholesterolemia that lack receptors. The addition of a mixture of 25-hydroxycholesterol and cholesterol suppressed squalene synthetase equally well in normal and mutant fibroblasts. Coupled with previous data, the current findings indicate that cholesterol derived from LDL regulates at least two enzymes in the cholesterol synthetic pathway in fibroblasts: (i) its primary action is to rapidly suppress 3-hydroxy-3-methylglutaryl coenzyme A reductase [mevalonate:NADP(+), oxidoreductase (CoA-acylating), EC 1.1.1.34], which reduces mevalonate production by 95% within 8 hr, and (ii) its secondary action is to slowly suppress squalene synthetase. The LDL-mediated suppression of squalene synthetase does not regulate de novo cholesterol synthesis; it occurs after 3-hydroxy-3-methylglutaryl coenzyme A reductase is already suppressed. Rather, we hypothesize that it may function to allow the pool size of farnesyl pyrophosphate to be maintained in the presence of LDL so that low levels of mevalonate can be shunted preferentially into nonsterol products, such as ubiquinone-10 and dolichol. This mechanism may explain the earlier observation that the synthesis of ubiquinone-10 in fibroblasts proceeds at a normal rate in the presence of LDL despite a 95% decrease in mevalonate production.

Cells, Cultured↗
PubMed1979

Solubilization of the low density lipoprotein receptor.

The low density lipoprotein (LDL) receptor was solubilized from membranes of bovine adrenal cortex and cultured human cells by incubation with the nonionic detergent octyl-beta-D-glucoside. Receptor activity released into the 100,000 x g supernatant was assayed by a solid-phase procedure: an aliquot of the soluble extract was removed, the detergent was diluted below its critical micellar concentration, causing the receptor to precipitate as a lipid-protein aggregate; the precipitate was collected by centrifugation and incubated with (125)I-labeled LDL ((125)I-LDL); and the receptor-bound (125)I-LDL was separated from free (125)I-LDL by filtration. The (125)I-LDL binding site that was precipitated from the soluble extract of bovine adrenocortical membranes appeared to be the same as the functional LDL receptor of cultured bovine adrenocortical cells and human fibroblasts. It exhibited high affinity and specificity (affinity for LDL more than 200-fold greater than for acetylated LDL, methylated LDL, or high density lipoprotein), dependence on calcium, and susceptibility to destruction by Pronase. The amount of (125)I-LDL binding activity in solubilized membranes from cultured cells was proportional to the number of receptors on the surface of the intact cells. Thus, the number of solubilized receptors was 1/20th of normal in mutant fibroblasts from a subject with homozygous familial hypercholesterolemia and was 1/4th of normal in human epithelioid carcinoma A-431 cells when they were grown in the presence of 25-hydroxycholesterol plus cholesterol. While in the soluble form in the presence of octyl-beta-D-glucoside, the LDL receptor can be carried through several steps of purification.

Adrenal Cortex↗
PubMed1979

Demonstration of low density lipoprotein receptors in mouse teratocarcinoma stem cells and description of a method for producing receptor-deficient mutant mice.

Familial hypercholesterolemia, a widespread human genetic disorder implicated in vascular and coronary disease, has had no laboratory animal counterpart that would enable the pathogenesis to be analyzed and drugs to be tested in vivo. The primary lesion in some patients is known to occur in the cells' initial handling of the major cholesterol-carrying lipoprotein of plasma. It entails a deficiency in the specific cell surface receptor that binds low density lipoprotein (LDL), with a consequent alteration in the control of cholesterol metabolism. The present study was undertaken to devise a practical scheme for producing, from developmentally versatile mouse teratocarcinoma stem cells, whole-animal models with a comparable genetic lesion. This requires first learning whether the tumor stem cells in culture express LDL receptors, and next establishing a selection or screening procedure to identify receptor-deficient mutants in mutagenized cell cultures. The results show that the teratocarcinoma cells do in fact have specific high-affinity LDL receptors which are similar to those reported for fibroblasts and the parenchymal cells of specialized tissues and different from those of phagocytic cells. Sterols suppressed the otherwise efficient binding, internalization, and degradation of LDL ((125)I-labeled) by the cells. Acetylation of LDL blocked the binding. Only LDL and not high density lipoprotein (HDL) was bound. After LDL uptake and degradation, the liberated cholesterol led, as expected, to increased cholesteryl ester formation; it also suppressed activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase [HMG CoA reductase; mevalonate: NADP(+) oxidoreductase (CoA-acylating), EC 1.1.1.34], the rate-limiting step in cholesterol biosynthesis. Cells with LDL receptors were readily visualized by administering a fluorescent derivative of LDL; in the fluorescence microscope, labeling was seen in all cells. Cells with experimentally depressed receptors, yielding little fluorescence, were separable from those with normal fluorescence in the fluorescence-activated cell sorter. Thus, two methods for isolating receptor-deficient cells from mutagenized cultures are now available, either by visual recognition of low-fluorescing or nonfluorescing colonies in culture plates or by electronic cell sorting. Such mutants in an appropriate line of teratocarcinoma cells can then be passaged into blastocysts for full somatic tissue differentiation and germ-line development into mice.

Animals↗
PubMed1979

Receptor-mediated endocytosis: insights from the lipoprotein receptor system.

The low density lipoprotein (LDL) receptor system coordinates the metabolism of cholesterol, an essential component of the plasma membrane of all mammalian cells. Study of this system has led to an enhanced understanding of the cellular basis of cholesterol homeostasis. It has also brought into focus an important mechanism of metabolic regulation--the process of receptor-mediated endocytosis. In this article, we first describe the receptor-mediated endocytosis of LDL, a sequence of events in which receptor binding and internalization are coupled in specialized regions of the plasma membrane called coated pits. Second, we trace the cellular functions of the cholesterol derived from internalized LDL. Third, genetic evidence is presented to indicate that both the binding and internalization of LDL are mediated by a single receptor molecule that contains two active sites, one mediating binding and the other internalization. Finally, the characteristics of the LDL receptor system are used to suggest models for receptor systems in general.

Adolescent↗