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At least 19 recordsLinked to original sources
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↗
PubMedDate not supplied

Colpocytograms and maternal serum placental cystine aminopeptidase, tissue cystine aminopeptidase, alkaline phosphatase and heat stable alkaline phosphatase activity in monitoring the last four weeks before delivery in high-risk pregnancy.

On the basis of the results of serial enzyme and cytohormonal assays in the last lunar month of gestation in 232 pergnant patients with high-risk pregnancy, it has been shown that the "at term" and inflammatory smears, which persist for over five days before labor, and post-partum" smears, significantly correlate with abnormal (low or decreasing) results of serum placental cystine aminopeptidase activity and with the pathologic course of pregnancy and labor as well as with the poor neonates' condition. The average serum placental and tissue cystine aminopeptidase determinations were the lowest in women with "post-partum" smears or persisting "at term" smears. These activities reached their highest they temporarily decreased. The oxytocinase activity curves in women with cytolytic smears were similar to those in patients with the "before term" smear patterns, which persisted before delivery. The average oxytocinase activity in women with the inflammatory smears was at first the highest and later it decreased most rapidly of all the groups under consideration. The maternal serum alkaline phosphatase and its heat-stable fraction in pregnant patients with "post-partum" and persisting "at term" smears were at first the lowest and just before labor the highest of all the cytologic pregnancy patterns. Colpocytograms confirmed their high prognostic value when compared with the enzyme tests of placental function.

Alkaline Phosphatase↗
PubMed1977

Factors controlling the nonprotein cystine content of cystinotic fibroblasts.

The cystine content of cystinotic fibroblasts increases with the length of time in cultivation. Four of five cystinotic cell strains showed an increase in cystine content with increased passage number. Cystinotic fibroblasts did not increase in cell number after 3 days in dialyzed fetal bovine serum. However, their cystine content increased almost 2-fold on a per cell number basis. Cystinotic cells incubated in cystine-free medium lost approximately 50% of their free cystine over a period of 12 hr and subsequently remained at about this level for 12 additional hr. Treatment of cystinotic cells with 1.0 mM dithiothreitol in complete medium reduced their free cystine content to about 25% of the initial level in 5 hr. The free cystine remained at this level after incubation overnight incystine-free medium without dithiothreitol. When dithiothreitol is added in the presence of a cystine-free medium, even more free cystine is removed from cystinotic cells (90%), and the free cystine content remains at this low level for as long as 48 hr if the cells are kept in a cystine-free medium. Cystinotic cells depleted of more than 50% of their intracellular free cystine by incubation in cystine-free medium reaccumulate cystine rapidly after replacement of cystine-containing medium. When cystinotic cells were depleted of their free cystine by treatment with dithiothreitol in a cystine-free medium and were then replaced in complete medium the intracellular free cystine reaccumulated rapidly, regaining its initial value in about 4 hr. The intracellular free cystine content found after 10 hr in complete medium reflected the cystine content of the medium. Cells in medium containing 0.266 mM cystine reaccumulated almost 60% more cystine than cells in medium with 0.066 mM cystine. When cystinotic and normal control fibroblasts were incubated for 2, 4, and 24 hr in either [35S]methionine or [35S]cystathionine, no radioactivity was recovered as cystine, cysteine, or glutathionine.

Cells, Cultured↗
PubMed1977

Patterns of cystine reduction by fibroblasts from normal and cystinotic children.

The possibility that the enzymatic reduction of cystine involves a multi-enzyme system led to re-evaluation of cystine reduction by fibroblasts from normal and cystinotic patients. Lineweaver-Burk plots of data with extracts of a normal cell line, representative of seven normal cell lines, under conditions of increasing cystine with variable levels of reduced glutathione (GSH) resulted in a two-limbed curve above 100 micronM cystine. Two cell lines from children with nephropathic cystinosis containing 1-6 micronmol half-cystine/g protein gave a family of curves similar to those of the normal. With six fibroblast lines containing more than 6 micronmol half-cystine/g protein, increasing cystine resulted in a family of lines without two-limbed curves. Plots of the data as activity against increasing cystine concentrations at ratios of cystine to GSH of 1:2 and 1:1 showed that two of the three lines from cystinotic subjects reduced cystine at a faster rate than the normal line. The third line from a cystinotic patient reduced cystine at a slightly slower rate when the substrate concentration in the assay was less than 80 micronM cystine. When the cystine to GSH ratio was maintained at 2:1, normal cells showed a linear increase in the rate of cystine reduction up to 100 micronM cystine, no increase in the rate between 100 micronM and 200 micronM cystine, and an increase again when the concentration of cystine was raised above 200 micronM. Such a stepwise phenomenon was absent with six cell lines containing more than 6 micronmol half-cystine/g cellular protein. A possible mechanism of control of cystine reduction is discussed.

Cell Line↗
PubMed1979

Elevated cystine levels in cultured skin fibroblasts from patients with I-cell disease.

Cultured skin fibroblasts from patients with I-cell disease (mucolipidosis II) exhibit multiple deficiency of acid hydrolase activities associated with a defect in the mechanism of packaging of these enzymes into lysosomes. The authors have examined such cells to ascertain whether the impairment of lysosomal function is of so broad a nature as to result in the storage of the amino acid cystine in a manner similar to that seen in cells derived from patients with cystinosis, an unrelated lysosomal storage disease of unknown etiology. Of 10 I-cell lines examined by automated amino acid analysis, seven were found to possess abnormally high levels of total free cyst(e)ine (i.e., greater than 1 nmole 1/2 Cys/mg protein). The mean half-cystine content of those I-cell lines subjected to multiple analysis ranged from 3-10 nmole/mg protein. levels which are comparable to those seen in homozygous cystinotic cells. The cystine content of several of these lines appeared to increase with subculture. Cultured fibroblasts from two patients with the biochemically similar, but clinically less severe, mucolipidosis III (pseudo-Hurler polydystrophy) exhibited normal to marginally elevated levels of cystine, whereas cells from individuals with three different mucopolysaccharide storage disorders contained normal levels of the amino acid. It was concluded that cystine, and not cysteine, was the predominant form of this amino acid in these cells, because previous reaction of I-cell extracts with N-ethylmaleimide did not alter the observed cystine levels. The further identification of excess cystine in these cells was corroborated by analytical results obtained with a highly specific cystine-binding protein method as well as by high-voltage electrophoresis of extracts from cells pulsed with 35S-cystine. Comparative analysis of intracellular amino acids in normal and I-cell fibroblasts indicated that the elevation of csystine seen in the latter was unique to this amino acid and did not reflect a generalized increase in the total free amino acid content of these mutant cells.

Cell Line↗
PubMed1975

Utilization of L-cystine by the gamma-glutamyl transpeptidase-gamma-glutamyl cyclotransferase pathway.

Cystine is a good acceptor of the gamma-glutamyl group of gamma-glutamyl donors in the reaction catalyzed by gamma-glutamyl transpeptidase. The product of the enzymatic reaction and an authentic sample of gamma-glutamylcystine were shown to exhibit identical chromatographic and electrophoretic behaviors; acid hydrolysis gave equimolar amounts of cystine and glutamate. In studies with two gamma-glutamyl donors, apparent Km values in the neighborhood of 0.3 mM were found for L-cystine; these values are not far from the concentrations of L-cystine in mammalian blood plasma. At an amino-acid acceptor concentration of about 0.5 mM, L-cystine is somewhat more active than L-glutamine, and much more active than L-cystein. L-gamma-Glutamyl-L-cystine was found to be a good substrate of gamma-glutamyl cyclotransferase. These observations thus indicate that L-cystine is a very active substrate of the gamma-glutamyl transpeptidase-gamma-glutamyl cyclotransferase pathway. In relation to the hypothesis that the gamma-glutamyl cycle functions in animo-acid transport, it may be significant that glutathione (which is the most abundant intracellular form) is a much better gamma-glutamyl donor than glutathione disulfide, while the predominant extracellular form-cystine-is a much better gamma-glutamyl acceptor substrate than cystein.

Acyltransferases↗
PubMed1977

Cystinotic fibroblasts accumulate cystine from intracellular protein degradation.

Fibroblasts derived from patients with cystinosis, an autosomal recessive condition, accumulate the disulfide amino acid cystine within lysosomes. The metabolic defect leading to the cystine accumulation and the source from which the cystine is derived are unknown. In this report we present data showing that cystine in these cells accumulates from the degradation of endogenous protein. This conclusion is based upon: (i) no demonstrable synthesis of cystine from serine; (ii) no difference in cystine reaccumulation between glutathione-depleted and non-glutathione-depleted cystinotic cells; (iii) recovery of labeled cystine only when the protein pool is labeled; (iv) reversible inhibition of cystine reaccumulation by known inhibitors of lysosomal protein degradation (chloroquine and NH4Cl).

Biodegradation, Environmental↗
PubMed1978

Cystine reductase in the dimorphic fungus Histoplasma capsulatum.

Organo-sulfur compounds favor the transition of mycelia of Histoplasma capsulatum to the yeast form (6, 8). Investigation of the role of cystine in the transition revealed that the two phases concentrated this amino acid at comparable rates and that mutants defective in the uptake of cystine were still able to undergo the transition normally. Uptake of cystine is therefore probably not a requirement for transition to or maintenance of the yeast phase. Both phases contained a reduced nicotinamide adenine dinucleotide phosphate-dependent glutathione reductase; but a reduced nicotinamide adenine dinucleotide-dependent cystine reductase was detectable only in the yeast phase. The cystine reductase appeared early in the transition of mycelium to yeast. Treatment of mycelia with p-chloromercuriphenylsulfonic acid, which prevented the transition to yeast, had no effect on cystine uptake but strongly inhibited the cystine reductase. These results suggest that cystine reductase may provide reduced sulfhydryl groups involved in the transition of mycelium to yeast.

4-Chloromercuribenzenesulfonate↗
PubMed1977

Some chemical and nutritional properties of feather protein isolates containing varying half-cystine levels.

Feather (keratinous) protein isolates containing 2.8 and 7.2% half-cystine were prepared. Solubility of the former increased to 100% between pH 6 and 12, whereas, that of the latter reached only 2.5% at pH 12. Tests showed that mixtures of sodium dodecyl sulfate and 2-mercaptoethanol were needed to completely solubilize the high half-cystine protein, and that sodium dodecyl sulfate alone or in combination with urea and/or 2-mercaptoethanol increased solubilization of the low half-cystine product. The rates of these reactions are further increased by heat. Dry heat denatured the low half-cystine isolate more readily than the high half-cystine product; moist heat denatured both at a similar rate. Gel electrophoretic properties were unique for each keratinous product. Only the low half-cystine isolate ahd desirable functional properties in that it formed thick, viscous mayonnaise-like emulsions and desirable foams. Functional properties of this isolate were improved dramatically by adjusting the pH from 5.0 to 8.2 or by a two-step change from pH 5.0 to 4.0 to 8.2. Apparent nitrogen digestibility of the two keratinous isolates was greater than 90% as measured by rat growth and by pepsin-HCl digestion.

Amino Acids↗
PubMed1978

Methionine-cystine interrelations in chicks fed diets containing suboptimal levels of methionine.

Studies were conducted with chicks on the interrelationship between cystine and methionine in either crystalline amino acid or wheat-peanut meal diets containing suboptimal levels of these two amino acids. The crystalline amino acid basal diet contained 0.2% DL-menthionine and 0.2% L-cystine whereas the wheat-peanut meal diet contained 0.2% methionine and 0.26% cystine. Marked improvements in weight gain and feed efficiency were observed when these diets were supplemented with 0.2 to 0.6% DL-methionine. When similar levels of L-cystine were added to the basal diets containing 0.2% methionine, chick growth was depressed. When the diets contained 0.4% methionine, the growth depressing effect of cystine was not observed. These results point to the existence of an antagonism of cystine on methionine utilization when the dietary level of methionine is suboptimal.

Amino Acids, Sulfur↗
PubMed1977

On the cysteine and cystine content of proteins. Differences between intracellular and extracellular proteins.

Analysis of published data on the cysteine and half-cystine content of proteins indicates that most intracellular proteins may be classified as sulfhydryl proteins (those containing cysteine but little or no half-cystine) and that such sulfhydryl proteins have a low cysteine content. The mean systeine content found for 32 intracellular mammalian proteins was 1.6% and intracellular proteins of many bacteria have similar or lower values. Extracellular mammalian proteins are primarily disulfide proteins (those containing half-cystine but little or no cysteine) have a high half-cystine content, the mean value found for some 34 extracellular mammalian proteins being 4.1%. This is contrasted with many of the extracellular proteins from facultative bacteria which are cyst(e)ine-free proteins, being lacking in both cysteine and half-cystine. These and related observations are interpreted in terms of the evolution of life in a reducing atmosphere and the subsequent transition to an oxidizing environment. It is suggested that disulfide proteins evolved primarily after the accumulation of oxygen in the atmosphere.

Bacterial Proteins↗
PubMed1978

Effects of cystine or glutamine restriction on human diploid fibroblasts in culture.

Amino-acid restriction was studied using a strain of human diploid fibroblasts (HDF) isolated from fetal skin. HDF populations were maintained at reduced proliferation rates by lowering cystine or glutamine concentrations of Eagle's MEM. Effects of this treatment on mean cell diameters, total cell protein and specific activity of acid phosphatase were assessed. Threshold levels of cystine required for maintenance were found to be markedly influenced by type and/or batch of serum used irrespective of their free cystine content. A 96-hr exposure of passage 25 cells to medium 0.01 or 0.005 mM in cystine resulted in an increased mean cell diameter and a greater heterogeneity of cell size. This was accompanied by an increase in the total cellular protein. A 48-hr exposure, followed by return to control serial cultivation, induced persistent change in mean cell diameter without affecting the total life span (49 passages over 165 days). The mean size of untreated cells increased with serial passage reaching a size similar to treated cells only at passage 44. Acid-phosphatase specific activities were higher in cells maintained under conditions restrictive in cystine. None of the above changes were observed when glutamine concentrations were reduced to 0.0025 mM, a level required to inhibit division rates. The possible relevance of these findings to the phenomenon of in vitro cell senescence is discussed.

Acid Phosphatase↗
PubMed1978

Conformation of L-cystathionine, a carba analog of cystine, and stereochemistry of hormone-receptor interactions.

The conformation of L-cystathionine, a carba analog of L-cystine, has been studied in the solid state using X-ray diffraction techniques. Crystal of L-cystathionine are tetragonal, space group P41 with cell constants a = 6.691(1) A, c = 21.998(3) A and Z = 4. From diffractometer data to the limit of 2theta = 162 degrees for Cukalpha, the structure was refined using full-matrix least-squares to an R value of 0.061. L-Cystathionine is isostructural chemically to L-cystine and its crystal structure is isomorphous to tetragonal L-cystine (Chaney, M.O. and Steinrauf, L.K. (1974) Acta Crystallogr. 1330, 711--716). The crystal structure of L-cystathionine is disordered, leading to two slightly differing conformers of L-cystathionine (each with half occupancy) with same helical sense but running in opposite directions and occupying the locations of L-cystine molecules in tetragonal L-cystine structure. Their conformational similarity, even when no sterical constraints such as cyclization are present, offers an explanation of the activities of the carba analogs of neuro-hypophysial hormones in terms of the structural integrity of the disulfide-like bridges.

Cystathionine↗
PubMed1976

Complete tyrosine assignments in the high-field 1H nuclear magnetic resonance spectrum of bovine pancreatic trypsin inhibitor selectively reduced and carboxamidomethylated at cystine 14-38.

The low-field portions of the 250-MHz 1H nuclear magnetic resonance spectra of native and chemically modified basic pancreatic trypsin inhibitor have been studied as a function of pH over the range pH 5-13. In derivatives selectively reduced and carboxamidomethylated at cystine 14-38, resonances associated with 15 of the 16 protons of the aromatic rings of the four tyrosines of the inhibitor have been located and assigned to specific tyrosyl residues. Titrations of pH yielded pK's for tyrosines 10, 21, 23, and 35 in the modified inhibitor of 9.9, 10.6, 11.6, and 11.0, respectively. Resonances associated with the three nitrotyrosine 10 protons of the mononitrated derivative and the six nitrotyrosine 10 and 21 protons of the dinitrated derivative have been similarly located, assigned, and titrated, yielding pK's for nitrotyrosines 10 and 21 of 6.5 and 6.4, respectively. Previously reported results for derivatives with cystine 14-38 intact have been revised on the basis of new data. Comparison of these revised results with the new data for derivatives with modified cystine 14-38 reveals no changes in pK's for any tyrosine or nitrotyrosing ring and no changes in chemical shift for resonances of nitrotyrosine 21 or tyrosines 21 and 23. However, modification of cystine 14-38 causes significant changes in chemical shifts of resonances of the nearby nitrotyrosine 10 and tyrosine 10 and 35 rings. Tyrosine 35 remains relatively immobile, rotating less than 1600 times/s at 25 degrees C for pH's in the range 5-13.

Animals↗
PubMed1977

Renal handling of dibasic amino acids and cystine in cystinuria.

1. The effect of intravenous infusion of L-lysine and L-arginine on the tubular reabsorption of dibasic amino acids and cystine was studied in normal individuals and in homozygous and heterozygous subjects with cystinuria. 2. The control subjects reabsorbed almost all filtered lysine and arginine until the filtered load was elevated about fourfold. With further increased loads the tubular reabsorption began to fall and tended to approach a maximum reabsorption rate. By contrast, the homozygous subjects could not reabsorb the elevated amino acid beyond the endogenous capacity until the filtered load was increased seven- to ten-fold. When the filtered load was further increased, tubular reabsorption proceeded at the normal rate in the cystinuric patients. 3. These findings may be explained by a low-capacity transport system, which acts at low substrate concentrations, being defective in the cystinuric subjects, while a high-capacity transport system, which predominates at high substrate concentrations, remains intact. 4. Lysine and arginine infusion depressed the percentage tubular reabsorption of other dibasic amino acids and cystine both in the control and the cystinuric subjects. In the control subjects the amino acid infusion caused a gradual linear fall in the fractional reabsorption of the dibasic amino acids and cystine, whereas the depressed reabsorption of the dibasic amono acids in the cystinuric patients returned to that observed under the endogenous condition when the filtered load was high. The amino acid load caused only a gradual decrease in cystine reabsorption in the cystinuric patients. 5. In the heterozygous subjects the slope of the titration curves and the depression of the tubular reabsorption were intermediate between those of the control and homozygous subjects.

Adolescent↗