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At least 19 recordsLinked to original sources

PubMed1981

Cystine crystalluria and urinary saturation in cystine and non-cystine stone formers.

It has been suggested recently that the first step in the formation of calcium oxalate stones appears to be crystallisation. This step is said to depend on the state of saturation of the urine. This hypothesis was checked in cystine stone formers. Cystine crystalluria was found in 83% of 24 urine samples from cystine stone formers (CSF) but in one of the 400 control samples and appears to be a good guide in the diagnosis of cystine lithiasis. Urinary cystine saturation was constantly higher in CSF than in non-cystine stone formers (NCSF) who exhibited undersaturated urine with respect to cystine. There was almost no overlap between these 2 groups. Crystals were never found in undersaturated urine and were always present when the saturation was above 1. There appears to be a good correlation between the level of urinary saturation and the presence of crystalluria and there is no need for any additional factor such as a defective inhibitor. The study underlines the limits of a therapeutic regimen of a high fluid intake and alkalinisation of the urine.

Crystallization↗

PubMed1976

Metabolism of cystine by Merino sheep genetically different in wool production IV. Rates of entry of cystine into plasma, measured with a single intravenous injection of L-[35S]cystine, and the subsequent incorporation of 35S into wool fibres.

Ten, 2-year-old Merino ewes from a flock selectively bred for high clean fleece weight (Fleece Plus) and ten from a flock bred for low clean fleece weight (Fleece Minus) were randomly divided between two dietary treatments: 600 or 1100 g/day of pelleted lucerne hay. After 14 weeks, each ewe received an intravenous injection of L-[35S]cystine (66-4 muCi). Venous blood samples were collected at 15 specified times until 8 h after the injections, and wool fibres were plucked until 65-75 days after the injections. Protein-free filtrates prepared from blood plasma were bulked within sample times for ewes from the same flock and dietary treatment. Equations relating the specific radioactivity of free cystine isolated from the bulked filtrates to time after injection contained three exponential terms. The entry rate and pool size of cystine estimated from these equations were greater in Fleece Minus than in Fleece Plus ewes (by 25 and 44% respectively for entry rate and pool size). Both traits were also higher in ewes offered 1100 g lucerne/day than in those offered 600 g/day (58-7 v. 33-9 mg/h for entry rate and 19-2 v 11-8 mg for pool size). The concentration of free cystine in plasma was greater in ewes offered 1100 g lucerne/day (3-0 v 2-1 mg/1; P less than 0-05), and greater in Fleece Minus ewes (3-0 v. 2-1 mg/l; P less than 0-05). The percentage of the injected radioactivity recovered in the wool clipped to day 70 post-injection differed between genotypes and between dietary treatments (P less than 0.05), being greater in Fleece Plus than in Fleece Minus ewes, and greater in those offered 1100 g lucerne/day than in those offered 600 g/day. The relationships between 35S incorporated per 1000 fibres (R) and time after injection (t) were best fitted by equations of the form (formula: see text). For all sheep, n = 3. The coefficient of the second term was significantly greater (P less than 0-05) in ewes offered 1100 g lucerne/day, whilst the constant of this term was significantly greater in Fleece Minus ewes. The specific radioactivities of cystine incorporated into wool fibres (SRf) during various intervals of time after injection were derived from these equations and from the measured rates of output of cystine in wool. The equations computed to relate SRf to time after injection (t) were of the form (formula: see text). Again there were three components. The coefficient of the third component was significantly greater (P less than 0-05) in ewes offered 1100 g lucerne/day, whilst the constant of the second term was significantly greater in Fleece Minus ewes.

Animals↗

PubMed1975

Hormone and enzyme assays in pregnancy. V. A rapid method for measuring the placental cystine-aminopeptidase using 1-cystine-bis-1-cystine-bis-p-nitroanilide-nitroanilide as substrate.

A rapid and simple method for determination of the placental cystine-aminopeptidase (P-CAP) activity in plasma is presented. The enzyme-catalysed hydrolysis of the substrate, 1-cystine-bis-p-nitroanilide, is followed in a spectrophotometer by reading the absorbance of the product p-nitroaniline at 380 nm. The absorbance increases linearily with time after a lag-period of 30 seconds to 5 min. The reaction is followed for about 10 min and the increase in absorbtion per min is calculated from the linear part of the absorbtion curve. The test could also be performed by taking 2 readings at about 5 min intervals. In the studies of the enzyme kinetics a competitive inhibitor of the reaction was found in plasma. The amount of the inhibitory substances seemed to be nearly constant in the plasma samples studied from normal pregnant women as well as in plasma samples with high enzyme activity (twin-pregnancy) and low enzyme activity (severe pre-eclampsia). The normal enzyme activity pattern showed an increase from about 210 days of pregnancy and towards the term. A coefficient of correlation of plus 0.83 with the more time consuming method using 1-cystine-di-beta-naphtylamide as substrate was found. It was concluded that the present method could replace the method described by Babuna & Yenen (1966) at least from about 210 days of pregnancy and where a rapid answer is necessary.

Adult↗

PubMed1984

Comparative study of cystine clearance in cystinotic and I-cell fibroblasts upon exposure to cystine dimethyl ester.

I-cell fibroblasts can accumulate cystine at levels comparable to those seen in homozygous cystinotic fibroblasts. Cystine accumulation in cystinosis is accounted for cystine clearance defect in situ. To unravel the question whether the same clearance defect or two different mechanisms cause cystine accumulation in I-cell disease, we used the cystine loading technique upon exposure of skin fibroblasts to radioactive cystine dimethyl ester. Normal, cystinotic and I-cell fibroblasts were exposed to radioactive cystine dimethyl ester, and the clearance of the generated radioactive cystine was measured. Cystinotic cells showed a marked defect in cystine clearance in situ, as compared to normal fibroblasts. In I-cell fibroblasts, we observed slow hydrolysis of cystine dimethyl ester to cystine, indicating low esterase activity, but no defect in clearance of the generated cystine. Cysteine production from the exogenous cystine dimethyl ester, presumably by cytoplasmic hydrolysis of the generated cystine, is normal in I-cell fibroblasts. Thus, our results indicate that, unlike cystinosis, there is no cystine clearance defect in situ for cystine in I-cell disease, and probably unrelated mechanisms cause cystine storage in cystinosis and I-cell disease.

Cell Line↗

PubMed1982

Cystine accumulation and clearance by normal and cystinotic leukocytes exposed to cystine dimethyl ester.

Upon exposure to 0.25 mM cystine dimethyl ester, normal and cystinotic leukocytes accumulate substantially more intracellular cystine than is present endogenously in cystinotic cells. Leukocytes loaded by exposure to cystine dimethyl ester may have abnormally lucent and distended lysosomes, and the cystine is compartmentalized within the granular fraction of the cells. After the cells are exposed to cystine dimethyl ester, cystine clearance from normal leukocytes is much faster than from cystinotic cells. The ratios of labeled cysteine-N-ethylmaleimide to cystine are also greater in normals than in cystinotics 60 min after termination of loading. No overlap in ranges of cystine clearance half-times or cystine-N-ethylmaleimide to cystine ratios was observed in normal compared to cystinotic leukocytes. Limited experiments with fibroblasts exposed to cystine dimethyl ester suggest a correspondingly prolonged cystine clearance for cystinotic cells. These experiments provide evidence for defective clearance of cystine from cystinotic lysosomes in situ.

Cystine↗

PubMed1994

Intracellular distribution of cystine in cystine-loaded proximal tubules.

Cellular cystine loading with cystine dimethyl ester has been shown to inhibit transport in proximal convoluted tubules perfused in vitro and decrease the rate of oxygen consumption in suspensions of proximal tubules. The present study was designed to examine the intracellular distribution of cystine in this model of the Fanconi syndrome of cystinosis and to determine whether cystine or its degradation product, cysteine, is the cytotoxic agent in cystine-loaded rabbit proximal tubules. Tubules were incubated with 2 mmol/L cystine dimethyl ester for 10 min at 37 degrees C and subjected to cellular fractionation. The intralysosomal cystine content (272 +/- 125 nmol/mg protein) was significantly higher than that measured in the nucleus (8.7 +/- 2.0 nmol/mg protein) and cytosol (9.8 +/- 4.0 nmol/mg protein (p < 0.05). Electron micrographs of tubules loaded with cystine depicted large swollen lysosomes. To determine whether cystine or its breakdown product, cysteine, was the cytotoxic agent in tubules incubated with cystine dimethyl ester, the intracellular cystine and cysteine contents were measured and found to be 86.5 +/- 14.8 and 5.7 +/- 1.7 nmol/mg protein, respectively. These tubules had a 50% decrease in the rate of O2 consumption. To examine whether the increased level of intracellular cysteine played a role in this decrease in O2 consumption, we loaded tubules with 2 mmol/L cysteine methyl ester for 10 min. Despite an intracellular cysteine concentration of 59.6 +/- 5.8 nmol/mg protein, cysteine-loaded tubules had a rate of O2 consumption equal to that measured in control tubules. Thus, intracellular cystine loading significantly increases intralysosomal cystine content.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2001

Solid phase assay of urine cystine supersaturation in the presence of cystine binding drugs.

PURPOSE: We report a new kind of assay system for urine cystine supersaturation that is accurate in the presence of cystine binding thiol drugs. We measured the molar ratio of cystine dissolved per mole of drug. MATERIALS AND METHODS: Measured amounts of cystine crystals were incubated in buffer or urine for 48 hours with stirring. The solid phase remaining was pelleted by centrifugation, extracted into a high pH buffer and measured. D-penicillamine, tiopronin and captopril were added to determine their effect on solid phase dissolution. RESULTS: Total cystine calculated from urine and solid measurements closely matched the amounts of cystine weighed in, meaning that the assay system successfully recovered the total cystine from the 2 phases. Each drug dissolved solid cystine in a specific and fixed proportion to its molar concentration in the range of 0.2 to 0.4 mM. dissolution per mM. of drug. Solution measurements were not a reliable gauge to the actual amounts of cystine dissolved. CONCLUSIONS: Changes in solid phase cystine accurately reflect buffer or urine supersaturation when thiol drugs are present. The solid phase assay is a technically straightforward and reliable way of assessing cystine movement into and out of urine that avoids complexity of measurement and distortions of assay systems by drugs. This assay enables one to assess the level of drug effect and the need for a change in dosing.

Buffers↗

PubMed1997

Cystine levels, cystine flux, and protein catabolism in cancer cachexia, HIV/SIV infection, and senescence.

Patients with skeletal muscle catabolism (cachexia) fail to conserve the skeletal muscle protein and release large amounts of nitrogen as urea. Previous studies suggest that the threshold for the conversion of amino acids into other forms of chemical energy and the concomitant production of urea are regulated by the plasma cystine level and hepatic cysteine catabolism. Studies of plasma amino acid exchange rates in the lower extremities now show that healthy young subjects regulate their plasma cystine level in a process that may be described as controlled constructive catabolism. The term controlled describes the fact that the release of cystine and other amino acids from the peripheral tissue is negatively correlated with (certain) plasma amino acid levels. The term constructive describes the fact that the release of cystine is correlated with an increase of the plasma cystine level. The regulation of the plasma cystine level is disturbed in conditions with progressive skeletal muscle catabolism including cancer, HIV infection, and old age. These conditions show also a low plasma glutamine:cystine ratio indicative of an impaired hepatic cystine catabolism. In HIV+ patients and SIV-infected macaques, a decrease of the plasma cystine level was found to coincide with the decrease of CD4+ T cells.

Adipose Tissue↗

PubMed1989

[A cystine-containing short-chain peptide as a potential cystine source for parenteral nutrition].

For the first time, in vivo utilization of two highly soluble and stable cystine containing synthetic short chain peptides, N,N'-bis-L-alanyl-L,L-cystine and N,N'-bis-glycyl-L,L-cystine, was investigated in adult rats. Within 5 min after an intravenous bolus, blood samples were drawn (inferior vena cava) and plasma amino acid and peptide levels were determined using RP-HPLC (precolumn derivatization with 1-dimethylaminonaphthalene-5-sulfonylchloride). Both peptides were rapidly cleared from plasma (estimated elimination time: 4 min for the glycyl peptide and less than 2 min for the alanyl peptide). The initial high amounts of N-L-alanyl-L,L-cystine and N-glycyl-L,L-cystine as well as the prompt increase of the constituent free amino acids alanine, glycine and cystine strongly suggest that the peptide disappearance is mainly due to a very fast two-step hydrolysis in the extracellular compartment, presumably catalyzed by soluble and/or plasma membrane bound peptidases. The observed rapid hydrolysis may serve as first evidence that short chain peptides with C-terminal cystine residue may represent efficient sources of free cystine in parenteral nutrition.

Alanine↗

PubMed1995

Metabolic studies of rat renal tubule cells loaded with cystine: the cystine dimethylester model of cystinosis.

The cause of Fanconi syndrome in cystinosis is enigmatic. It has previously been shown that renal tubules could be loaded with cystine by incubating them with cystine dimethylester (CDE), mimicking the biochemical hallmark of cystinosis. Such tubules have impaired transport, decreased whole-cell O2 consumption, and substrate utilization. In this study, the metabolic disturbances in cystine-loaded renal tubule cells were further characterized. Isolated rat renal tubules were loaded with cystine by incubating them with 2 mM CDE for 10 min. This had no significant effect on total ATPase, Na(+)-K(+)-ATPase, or the ouabain-insensitive ATPase activity of renal tissue homogenates from these cystine-loaded tubules. Intracellular K was significantly lower in the cystine-loaded tubules (37 +/- 2 versus 47 +/- 3 nEq/mg; P < 0.008). Intracellular ATP was reduced by 39% in the cystine-loaded tubules (23.7 +/- 2.4 versus 38.1 +/- 3.3 nmol/mg of protein; P < 0.0025). CDE (2 mM) reduced isolated mitochondrial O2 consumption with glutamate as the substrate by 66% (4.7 +/- 0.7 versus 13.9 +/- 0.8 nm/min per mg of protein, P < 0.001) but had no effect on mitochondrial O2 consumption with succinate as the substrate. It was speculated that the impaired transport from cystine loading with CDE is secondary to a decrease in energy generation.

Adenosine Triphosphate↗

PubMed2003

The role of cystine knots in collagen folding and stability, part II. Conformational properties of (Pro-Hyp-Gly)n model trimers with N- and C-terminal collagen type III cystine knots.

In mature collagen type III the homotrimer is C-terminally cross-linked by an interchain cystine knot consisting of three disulfide bridges of unknown connectivity. This cystine knot with two adjacent cysteine residues on each of the three alpha chains has recently been used for the synthesis and expression of model homotrimers. To investigate the origin of correct interchain cysteine pairings, (Pro-Hyp-Gly)(n) peptides of increasing triplet number and containing the biscysteinyl sequence C- and N-terminally were synthesised. The possibilities were that this origin may be thermodynamically coupled to the formation of the collagen triple helix as happens in the oxidative folding of proteins, or it could represent a post-folding event. Only with five triplets, which is known to represent the minimum number for self-association of collagenous peptides into a triple helix, air-oxidation produces the homotrimer in good yields (70 %), the rest being intrachain oxidised monomers. Increasing the number of triplets has no effect on yield suggesting the formation of kinetically trapped intermediates, which are not reshuffled by the glutathione redox buffer. N-terminal incorporation of the cystine knot is significantly less efficient in the homotrimerisation step and also in terms of triple-helix stabilisation. Compared to an artificial C-terminal cystine knot consisting of two interchain disulfide bridges, the collagen type III cystine knot produces collagenous homotrimers of remarkably high thermostability, although the concentration-independent refolding rates are not affected by the type of disulfide bridging. Since the natural cystine knot allows ready access to homotrimeric collagenous peptides of significantly enhanced triple-helix thermostability it may well represent a promising approach for the preparation of collagen-like innovative biomaterials. Conversely, the more laborious regioselectively formed artificial cystine knot still represents the only synthetic strategy for heterotrimeric collagenous peptides.

Amino Acid Sequence↗

PubMed1984

Cystine accumulation and clearance in normal and cystinotic fibroblasts exposed to cystine dimethyl ester.

Exposure of cultured skin fibroblasts of normals and cystinotic patients to 0.5 mmol/l[35S]cystine dimethyl ester for 30 min resulted in an accumulation of cystine in excess to that naturally occurring in cystinotic skin fibroblasts. These equal levels of cystine accumulation achieved in both cystinotic and normal cells, permitted comparative experiments to look for differences in cystine disposal between normal and cystinotic cells. Cystinotic fibroblasts demonstrated very low cystine clearance with a lower ratio of cysteine-N-ethylmaleimide to cystine than normal. The results on cystinotic fibroblasts are consistent with those observed in leucocytes, suggesting that fibroblasts can be useful in further studies to elucidate the clearance defect of cystine in cystinosis as well as its potential in antenatal diagnosis.

Cells, Cultured↗

PubMedDate not supplied

Canine cystinuria: an extended study on the effects of 2-mercaptopropionylglycine on cystine urolithiasis and urinary cystine excretion.

A clinical study covering 1 to 6 years was undertaken during which 25 cystinuric dogs were orally treated with 2-mercaptopropionylglycine (2-MPG). The drug was effective at dissolving uroliths at a dose of approximately 40 mg kg-1 body weight. In 15 dogs with bladder uroliths, complete urolith dissolution was achieved on 9/17 occasions (53%). When 2-MPG was administered prophylactically at 30 mg/kg body weight, uroliths did not reform in 14 dogs (56%). In four dogs, uroliths re-formed during treatment, but dissolved when the dose of 2-MPG was raised to 40 mg kg-1 body weight. Six dogs were surgically treated, and in two of these animals the uroliths were found to consist of magnesium ammonium phosphate. Euthanasia was performed on six dogs during the study; three because of recurrent uroliths with urethral obstruction, and three because of aging. In one dog, uroliths were present in the bladder throughout the study. The purpose of the study was to propose a new strategy for individual treatment of cystinuric dogs. This was accomplished by measuring the urinary free cystine concentration and the mixed cysteine-2-MPG disulphide in a subgroup of 15 of the 25 dogs. To evaluate cystine excretion, morning samples of urine were used, and the cystine concentration was related to the creatinine concentration. For dose adjustment it was difficult to evaluate the effect of 2-MPG on urinary cystine excretion, especially when cystine uroliths were present. However, this variable was studied in order to identify dogs with a strong tendency for urolith formation during 2-MPG treatment. In some cases, urinary cystine excretion returned to normal with time, and in three dogs, 2-MPG treatment could be stopped after 1.5 to 3.5 years. In spite of no further treatment, urinary cystine was almost undetectable up to 2 years later, and the dogs did not develop any new uroliths. It was concluded that 2-MPG is a satisfactory alternative treatment for cystinuric dogs. It has a good prophylactic effect, shown as a change in the rate of urolith formation from on average 6 months before to 17 months during 2-MPT treatment. The drug was shown to have few side effects, and the dog owner drug compliance can be followed by measurement of the mixed 2-MPG-cysteine disulphide.

Animals↗

PubMed1990

Depletion of cystine in cystinotic fibroblasts by homocysteine. Synergism of cysteamine with various reducing agents in depletion of cystine from cystinotic fibroblasts.

The present study shows that homocysteine depleted cystine from cystinotic fibroblasts in vitro. No toxic effects were noted as judged by morphology and growth patterns. Efflux of radioactivity from cystinotic cells prelabeled with [35S]cystine was greater in homocysteine-treated cystinotic cells than in untreated controls. This radioactivity was found, by high voltage electrophoresis separation of effluxed products, to consist mainly of [35S]cystine, along with smaller amounts of [35S]homocysteine-cysteine mixed disulfide. When homocysteine and cysteamine were presented together to cystinotic cells at dose levels individually ineffective in removing cystine from these cells, a marked synergistic effect was observed and cystine content fell to 10% of that seen in untreated cystinotic fibroblasts. Similarly, synergistic effects of cystine depletion from cystinotic cells were demonstrated when cells were treated with a combination of cysteamine and dithiothreitol or glutathione. Incubation of cystinotic cells with homocysteine, dithiothreitol, or cysteamine in combination with vitamin C did not yield synergistic effects. The above findings suggest a novel way to probe metabolic processes in these mutant cells. Exploration of these synergistic effects may lead to more efficacious therapeutic protocols for cystinosis.

Ascorbic Acid↗

PubMed2003

Studies of urinary cystine precipitation in vitro: ontogeny of cystine nephrolithiasis and identification of meso-2,3-dimercaptosuccinic acid as a potential therapy for cystinuria.

Children with fully recessive (Type I/I) cystinuria have a high risk of stone formation in the first decade of life. To assess the tendency for cystine to precipitate in individual urine samples, we developed an in vitro assay in which radiolabelled cystine (4mM) was dissolved in urine at 37 degrees C after alkalization to pH 10. Samples were then brought to pH 5, cooled, and centrifuged. The % decrease in supernatant cpm was used as a measure of cystine precipitation (CP). CP varied widely among normal children (74%+/-34) whereas variability of repeated determinations on a single adult individual was modest (64%+/-3.3). The assay was used to compare various potential therapies for cystinuria. Precipitation of exogenous cystine from normal urine was strongly inhibited by addition of D-penicillamine (CP: 8%+/-3) or dimercaptosuccinic acid (DMSA) (CP: 5%+/-1), at urinary concentrations attained by standard oral doses of each drug. Mercaptopropionylglycine (MPG) was moderately effective (CP: 43%+/-9), whereas captopril was a weak inhibitor (CP: 63%+/-12). Precipitation of endogenous cystine (2191 micromol/L) from a cystinuric patient showed that DMSA and D-penicillamine were again highly effective compared to the other agents. In addition DMSA and penicillamine added to the same patient's urine reduced the free cystine by 50% (as measured by automated amino acid analyzer) whereas MPG and captopril had no effect. In conclusion, DMSA is comparable to D-penicillamine as an in vitro inhibitor.

Adolescent↗

PubMed2003

The role of cystine knots in collagen folding and stability, part I. Conformational properties of (Pro-Hyp-Gly)5 and (Pro-(4S)-FPro-Gly)5 model trimers with an artificial cystine knot.

In analogy to the cystine knots present in natural collagens, a simplified disulfide cross-link was used to analyse the conformational effects of a C-terminal artificial cystine knot on the folding of collagenous peptides consisting of solely (Pro-Hyp-Gly) repeating units. Assembly of the alpha chains into a heterotrimer by previously applied regioselective disulfide-bridging strategies failed because of the high tendency of (Pro-Hyp-Gly)(5) peptides to self-associate and form homotrimers. Only when side-chain-protected peptides were used, for example in the Hyp(tBu) form, and a new protection scheme was adopted, selective interchain-disulfide cross-linking into the heterotrimer in organic solvents was successful. This unexpected strong effect of the conformational properties on the efficiency of well-established reactions was further supported by replacing the Hyp residues with (4S)-fluoroproline, which is known to destabilise triple-helical structures. With the related [Pro-(4S)-FPro-Gly](5) peptides, assembly of the heterotrimer in aqueous solution proceeded in a satisfactory manner. Both the intermediates and the final fluorinated heterotrimer are fully unfolded in aqueous solution even at 4 degrees C. Conversely, the disulfide-crossbridged (Pro-Hyp-Gly)(5) heterotrimer forms a very stable triple helix. The observation that thermal unfolding leads to scrambling of the disulfide bridges was unexpected. Although NMR experiments support an extension of the triple helix into the cystine knot, thermolysis is not associated with the unfolding process. In fact, the unstructured fluorinated trimer undergoes an equally facile thermodegradation associated with the intrinsic tendency of unsymmetrical disulfides to disproportionate into symmetrical disulfides under favourable conditions. The experimental results obtained with the model peptides fully support the role of triple-helix nucleation and stabilisation by the artificial cystine knot as previously suggested for the natural cystine knots in collagens.

Amino Acid Sequence↗

PubMed1990

Effect of cystine loading and cystine dimethylester on renal brushborder membrane transport.

The effect of loading renal tubule cells with cystine was studied by incubating them with cystine dimethylester. Proline uptake into brushborder membrane vesicles isolated from the cystine loaded cells was not different from that observed into brushborder vesicles isolated from tubules incubated in buffer alone. Incubating brushborder membranes with 2 mM cystine dimethylester for 10 minutes reduced the uptake of proline by 27% after 15 seconds of incubation and by 21% after 60 seconds of incubation. There was no effect after 20 minutes of incubation. Pre-incubating brushborder membrane vesicles with cystine dimethylester had no statistically significant effect on the affinity of proline for the carrier, but did reduce the maximal rate of proline uptake by 49%.

Animals↗

PubMed1982

Cystine accumulation in cystinotic fibroblasts from free and protein-linked cystine but not cysteine.

The accumulation of cystine in cystinotic fibroblasts from free and protein-linked cystine has been investigated. Cystine is not accumulated from cysteine but is readily accumulated from cystine. The accumulation from free cystine does not occur as a result of pinocytosis or from the degradation of a rapidly metabolized protein pool. Further studies of the degradation of disulphide-containing proteins by these cells may aid understanding of the mechanisms of proteolysis.

Cell Line↗