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PubMed1995

Quantification of 5-fluorouracil incorporation into RNA of human and murine tumors as measured with a sensitive gas chromatography-mass spectrometry assay.

5-Fluorouracil (5FU) can exert its cytotoxic activity by either inhibition of thymidylate synthase or incorporation into RNA. The extent and importance of the latter in tumors of patients are not clear, due to the lack of sensitive and reproducible methods. RNA from 5FU-treated human WiDr colon tumor cells was isolated and [(14)CL]5FU incorporation into RNA was measured by traditional scintillation counting while that of nonradiolabeled 5FU was measured with the present, new method. For the latter purpose, isolated RNA was incubated with RNase, alkaline phosphatase, and uridine phosphorylase, resulting in a complete degradation of RNA, nucleotides, and nucleoside to 5FU. 5FU was then measured with gas chromatography coupled to mass spectrometry. For both methods RNA incorporation was 0.4 pmol/h/micrograms RNA at 25 microM 5FU while a similar time (up to 4 h) and concentration dependence (25 to 50 microM) were found. Reproducibility of the assay was more than 95%. In a murine colon tumor 5FU incorporation into RNA reached a peak of 10 pmol/micron RNA at 2 h after administration of the the maximum tolerated dose of 80 mg5FU/kg, which was retained until at least 72 h at 2.5 pmol/micron. In tumors from patients treated with 500 mg5FU/m(2) incorporation into RNA after 24 h amounted to 1.0-1.5 pmol/micrograms RNA. In conclusion, a novel approach, combining different sensitive and reproducible techniques, was established to measure 5FU incorporation into RNA in clinical tumor specimens enabling determination of its clinical relevance.

Animals↗

PubMed1996

Kinetics of protein farnesyltransferase: sigmoidal vs hyperbolic behavior as a function of assay conditions.

Protein farnesyl transferase (FTase) catalyzes the addition of a farnesyl isoprenoid to a conserved cysteine residue in Ras and several other key proteins involved in cell regulation. An assay technique commonly used to measure FTase activity involves vacuum filtration. This assay, which traps precipitated, radiolabeled prenylated proteins on a glass fiber filter for analysis by scintillation counting, was designed to be fast and accurate. In the case of FTase, substrate saturation curves generated by this assay technique using Ras as a substrate often show a lag at low Ras concentrations, resulting in curves with sigmoidal character. We have found that the sigmoidal behavior is due to the use of the filter binding assay and not to any inherent property of FTase. Specifically, the glass fiber filters do not adequately trap precipitated Ras proteins, especially at low concentrations. Addition of cytosol from either bovine brain or liver, or of purified tubulin to the FTase assay mixture prior to the precipitation step, results in the apparent formation of stable complexes of farnesylated Ras protein that can then be optimally trapped on the glass fiber filter. This appears to be at least in part due to the ability of tubulin to bind the prenyl protein reaction product. The ability to obtain accurate kinetics for the FTase using the standard filter binding assay should greatly enhance its use to accurately assess the properties of FTase inhibitors.

Alkyl and Aryl Transferases↗

PubMed1998

Detection and quantitation of heterotrimeric G proteins by fluorescence resonance energy transfer.

N-Methyl-3'-O-anthranoyl (mant) guanine nucleotide analogs are useful environmentally sensitive fluorescent probes for detection of heterotrimeric guanine nucleotide binding proteins. The mant derivative of GTP gamma S, mGTP gamma S, is synthesized and purified by modification of a method initially described by Hiratsuka (1983, Biochim. Biophys. Acta 742, 496-508). The binding affinity of mGTP gamma S for G proteins Gi and G(o) is comparable to that of GTP gamma S. The rate of binding is determined by the dissociation rate of the endogenously bound GDP. The large fluorescence increase observed upon mGTP gamma S binding to G protein is due, in part, to resonance energy transfer from tryptophans in the G protein to the mant guanine nucleotide. The magnitude of the fluorescence increase is dependent upon the concentration of G protein. Therefore, mGTP gamma S binding can be used to quantitate and locate G proteins during the protein purification process. This method is rapid compared to the [35S]GTP gamma S binding assay in that (i) the bound ligand does not need to be separated from the free ligand thus avoiding vacuum filtration and (ii) the time required to measure fluorescence in each sample is less than that required for scintillation counting. In addition, the use of radioactivity can be avoided. Thus, the mGTP gamma S binding assay for the detection of Gi and G(o) represents a rapid, reliable alternative to assays based on radiolabeled GTP gamma S binding or ADP-ribosylation with pertussis toxin.

Biopolymers↗

PubMed1998

Separation of radiolabeled orthophosphate and adenosine 5'-triphosphate by 20% polyacrylamide gel electrophoresis: an assay for brain microsomal Mg2+/Ca2+ ATPase activity.

Measuring orthophosphate is an important tool in biochemical analyses used to study membrane transport ATPases essential for calcium homeostasis. Current techniques involve extraction of radioactive phosphate with organic solvents, a technique that results in large quantities of hazardous radioactive waste. Other colorimetric assays are less sensitive and are complicated by interference of background absorbance from membrane tissue and unutilized ATP. This report describes a unique assay for the detection of inorganic phosphate and its application to the study of rat brain microsomal Mg2+/Ca2+ ATPase from a membrane fraction. The technique involves the separation of radioactive phosphate from unused gamma-radiolabeled ATP by resolution on 20% polyacrylamide gels. Both are visualized with X-ray film and quantitated by liquid scintillation counting after extraction from the gels. The assay can detect as little as 4.1 pmol of radiolabeled ATP and ATPase activity in 3.5 ng/microliter of membrane protein. This method offers the advantage of simultaneous quantitation of radiolabeled ATP and radioactive orthophosphate without the generation of large quantities of radioactive waste. The results demonstrate the development of a novel assay procedure for quantitating orthophosphate that is extremely sensitive, reproducible, and applicable to the study of any phosphate liberating enzyme.

Adenosine Triphosphate↗

PubMed1999

A sensitive and specific radiochromatographic assay of fatty acid amide hydrolase activity.

A radiochromatographic method has been set up in order to determine fatty acid amide hydrolase (FAAH) activity, based on reversed-phase high-performance liquid chromatography and on-line scintillation counting. The reaction products were separated using a C18 column eluted with methanol-water-acetic acid and quantitated with an external standard. Baseline separation of the acid product from the substrate was completed in less than 4 min, with a detection limit of 2.5 fmol arachidonic acid at a signal to noise ratio of 4:1. The method enabled to determine the kinetic constants (i.e., apparent Km of 2.0 +/- 0.2 microM and Vmax of 800 +/- 75 pmol. min-1. mg protein-1 toward anandamide) and the substrate specificity of human brain FAAH, as well as the extent of enzyme inhibition by some anandamide congeners. The femtomole sensitivity and the accuracy of the method allow detection and characterization of the activity of FAAH in very minute tissue samples or in samples where the enzymatic activity is very low.

Aged↗

PubMed1999

Buffer effects on EcoRV kinetics as measured by fluorescent staining and digital imaging of plasmid cleavage.

We have developed a protocol to quantify polymer DNA cleavage which replaces the traditional radiolabeling and scintillation counting with fluorescent staining and digital imaging. This procedure offers high sensitivity, speed, and convenience, while avoiding waste and error associated with traditional 32P radiolabeling. This protocol was used to measure cleavage of pBR322 plasmid DNA by EcoRV, a type II restriction enzyme. EcoRV was found to exhibit an order of magnitude difference in binding in two apparently similar buffers used in previous investigations. To determine the origin of this effect, we measured reaction kinetics in buffers of different chemical nature and concentration: Tris, bis-Tris propane, Tes, Hepes, and cacodylate. We found that buffer concentration and identity had significant effects on EcoRV reaction velocity through large changes in specific binding and nonspecific binding (reflected in the Michaelis constant Km and the dissociation constant for nonspecific binding Kns). There were only small changes in Vmax. The source of the buffer effect is the protonated amines common to many pH buffers. These buffer cations likely act as counterions screening DNA phosphates, where both the protonated buffer structure and concentration affect enzyme binding strength. It appears that by choosing anionic buffers or zwitterionic buffers with a buried positive charge, buffer influence on the protein binding to DNA can be largely eliminated.

Buffers↗

PubMed1999

Photometric assay for polynucleotide phosphorylase.

Polynucleotide phosphorylase (PNPase) is a prokaryotic enzyme that catalyzes phosphorolysis of polynucleotides with release of NDPs. It is also believed to play a key role in turnover of prokaryotic transcripts, thus regulating gene expression. At the moment, only radioisotopic methods are available for assaying PNPase in crude extracts; these involve incubating [32P]phosphate and poly(A) in the presence of the enzyme, separating [32P]phosphate from [32P]ADP, and quantifying ADP by scintillation counting. Photometric assay using pyruvate kinase and lactate dehydrogenase as auxiliary enzymes is not feasible in crude extracts because of endogenous ATPase activities, which regenerate ADP from the ATP released by pyruvate kinase. Here, we present a simple photometric assay that uses a cyclic detection system which, due to the sequential action of pyruvate kinase and hexokinase, results in an exponential increase of ADP and glucose 6-phosphate. Glucose 6-phosphate is then revealed by a glucose-6-phosphate dehydrogenase reaction. Based on the theoretical model, a linear increase in absorbance is predicted as a function of the square of the reaction time, with a slope proportional to PNPase activity. Experimental data confirmed the theoretical predictions and showed that the assay was quantitative and unquestionably specific. We also devised a simple procedure for determining absolute enzyme activities (expressed in micromoles of product formed per minute) using exact amounts of pure PNPase as internal standards.

Adenosine Diphosphate↗

PubMed1999

32P-postlabeling assay for the quantification of the major platinum-DNA adducts.

To allow more sensitive, selective, and routine analyses of platinum(Pt)-GG and -AG intrastrand cross-links we have significantly improved our quantitative (32)P-postlabeling assay (M. J. P. Welters et al. Carcinogenesis 18, 1767-1774, 1997). Instead of off-line scintillation counting we introduced an on-line flow radioisotope detector into the HPLC system. Furthermore, the isolation protocol for the adducts was significantly modified and optimized to reduce interfering background peaks that prevented quantification of low levels of the cisplatin-DNA adducts in white blood cells obtained from patients. Reduction of background signals was obtained by boiling the samples, followed by phenol/chloroform/isoamylethanol extraction after the DNA digestion step. The labeling efficiency for the adducts was increased by 40% by using Na-formate instead of NH(4)-formate for elution of the adducts from the strong cation-exchange columns. Finally, a calibration curve and quality controls were implemented. The labeling efficiencies were not different between the dinucleotides. The between- and within-run precision for the Pt-GG and Pt-AG adducts measured at the lower limit of quantification of 87 and 53 amol/microg DNA, respectively, was less than 20% CV. The adducts were stable in DNA stored for a 2-month time period at -80 degrees C. The assay is now routinely used for high-precision analyses of patient and cell line samples containing very low adduct levels.

Animals↗

PubMed2000

Quantitative radioisotopic determination of histidine decarboxylase using high-performance liquid chromatography.

We have developed a procedure for the accurate measurement of histidine decarboxylase in tissues expressing low levels of enzymatic activity. Briefly, histamine is enzymatically synthesized from [3H]-labeled histidine, followed by purification using high-performance liquid chromatography (HPLC) and quantitation by liquid scintillation counting. This method presents three advantages over previous techniques. First, prior to HPLC purification, excess precursor [3H]histidine is removed on an anion-exchange resin. Second, purification by HPLC is considerably more selective than that of classical cation-exchange gravity columns or organic solvent extractions. Finally, the accuracy of this method is improved by including non-radiolabeled histamine as internal standard, which is quantified by ultraviolet detection. This simple procedure allows highly sensitive and accurate determinations of histamine synthesis.

Animals↗

PubMed2000

Differential use of Alcian blue and toluidine blue dyes for the quantification and isolation of anionic glycoconjugates from cell cultures: application to proteoglycans and a high-molecular-weight glycoprotein synthesized by articular chondrocytes.

Alcian blue and toluidine blue dyes form complexes with anionic glycoconjugates (AG) such as proteoglycans (PG) and glycosaminoglycans (GAG). However, the Alcian blue-AG complexes do not readily dissociate, while the toluidine blue-AG complexes do so in salt solutions. This differential dissociation of the dye-AG complexes has been utilized in the analysis and isolation of radiolabeled AG elaborated by articular chondrocyte cultures incubated with the radiolabeled precursors of AG. For the rapid quantification of newly synthesized (35)S-labeled PG, small replicate aliquots of the radiolabeled culture media were applied directly to cellulose acetate strips, stained with Alcian blue and the stained immobilized radiolabeled PG was quantified by liquid scintillation counting. Comparison of anionic glycoconjugates quantified in the culture media employing toluidine blue and Alcian blue staining on cellulose acetate trips gave similar results. Staining on cellulose acetate strips using these two dyes is particularly suited for the simultaneous processing of large numbers of samples, as illustrated by the screening of the effects of biological materials and drugs on AG synthesis, in cultures labeled with [(35)S]-sulfate and [(3)H]-glucosamine. The Alcian blue and toluidine blue precipitation methods yielded similar results for the total AG recovered from the media of TGF-beta-stimulated chondrocytes. Electrophoretic analysis of toluidine blue- and Alcian blue-precipitated AG followed by autoradiography and Alcian blue staining in combination with silver nitrate demonstrated that both dyes yielded similar pattern of bands on gels. However, some AG from Alcian blue precipitate did not enter the gel, suggesting incomplete dissociation of Alcian blue-AG complex. The application of the toluidine blue precipitation method, in combination with enzymatic digestion of the GAG chains of the PGs, is illustrated by the isolation of a non-PG high-molecular-weight AG, as well as the PGs from the media of chondrocyte cultures stimulated by TGF-beta.

Alcian Blue↗

PubMed2002

Radiochemical malonyl-CoA decarboxylase assay: activity and subcellular distribution in heart and skeletal muscle.

Malonyl-CoA decarboxylase is the main route for the disposal of malonyl-CoA, the key metabolite in the regulation of mitochondrial fatty acid oxidation. We have developed a simple and sensitive radiochemical assay to determine malonyl-CoA decarboxylase activity. The decarboxylation of [2-14C]malonyl-CoA produces [2-14C]acetyl-CoA, which is converted to [2-14C]acetylcarnitine in the presence of excess L-carnitine and carnitine acetyltransferase. The positively charged radiolabeled product, acetylcarnitine, is separated from negatively charged excess radiolabeled substrate and the radioactivity measured by scintillation counting. Measurement of malonyl-CoA decarboxylase activities with this method gives values comparable to those obtained with assays currently in use, but has the advantage of being simpler and less labor intensive. We have applied this assay to rat skeletal muscle of different fiber-type composition and to rat heart. Malonyl-CoA decarboxylase activity (mU/g wet wt) correlates with the oxidative capacity of the muscles, being lowest in type IIb fibers (42.7 +/- 3.0) and highest in heart (1071.4 +/- 260), with intermediate activity in type IIa fibers (150.7 +/- 4.3) and type I fibers (107.8 +/- 7.6). Studies on subcellular distribution of malonyl-CoA decarboxylase activity in rat heart and rat skeletal muscle show that approximately 50 and 65% is localized to mitochondria, while 50 and 35% of the activity is extramitochondrial.

Animals↗

PubMed2002

A biotin capture assay for oligosaccharyltransferase.

Oligosaccharyltransferase (OST) catalyzes the en bloc transfer of dolichylpyrophosphate oligosaccharides to an asparagine residue found in the sequon Asn-Xaa-Thr/Ser of newly synthesized proteins. Currently the method most commonly used to monitor this reaction, involving multiple solvent extractions and HPLC, is extremely time consuming and tedious. Herein, we present the use of a biotinylated peptide as the acceptor substrate and dolichylpyrophosphate [3H]chitobiose as the donor substrate for the OST-catalyzed reaction. This allows for separation (avidin-agarose beads) and quantitative analysis (scintillation counting) of only the biotinylated glycopeptide product of the OST-catalyzed reaction. This new assay yields highly reproducible results in a rapid manner.

Biological Assay↗

PubMed1998

Estimation of the growth rate of mixed ruminal bacteria from short-term DNA radiolabeling.

A method based on 32P-labeling of DNA in short-term incubations was developed for estimating the growth rate of mixed rumen bacteria. A freeze/thaw procedure was optimized to quantitatively disrupt mixed rumen bacteria and extract bacterial DNA. The preliminary enzymatic lysis step, with lysozyme rather than proteinase K, sodium lauroyl sarcosine, and, to a lesser extent, sodium dodecyl sulfate (SDS) strongly improved cell disruption and DNA recovery rates. Sodium deoxycholate, CHAPS or Triton X-100 had no significant effect. Increasing the number of cycles or lowering the freezing temperature from -20 degrees C to -50 degrees C had no effect on DNA extraction efficiency while setting the thawing temperature at +60 degrees C rather than +37 degrees C slightly increased DNA yield but also increased its contamination with RNA. The method finally selected led to the lysis of at least 93% of cells and to the extraction of 85% of bacterial DNA. The kinetics of in vitro 32P incorporation into rumen bacteria DNA was then determined in batch incubations of strained rumen contents with no additional substrate. The curvilinear effects of the amount of 32P and the incubation time (5-15 min) on the DNA radioactivity were investigated by applying a Doehlert experimental design and fitting a second order polynomial model to data. The DNA radioactivity was linearly related to time (p<0.02) with other coefficients in the model being equal to zero (p>0.20). The incorporation of 32P into bacterial DNA was initiated approximately 70 s after the start of incubation. Taking into account the accuracy of scintillation counting, 10-15 min incubations, with 15 microCi 32P and 10 mL rumen contents per tube, appeared satisfactory for future studies.

Journal Article↗

PubMed1996

Differential effects of 3,5,3'-triiodothyronine on control and mdx myoblasts and fibroblasts: analysis by flow cytometry.

The possibility of differential effects of triiodothyronine (T3) treatment in vivo on myoblast and fibroblast cell proliferation was examined in control and mdx muscle cultures. Cell isolates were purified in a Percoll gradient, sorted by flow cytometry (light scatter), and characterized as myoblasts and fibroblasts using antiskeletal muscle myosin fluorescence. The two cell types were grown separately or remixed (1:1). Cultures were incubated with or without T3 (10(-9) M) for 19 h. Cells were either exposed to [3H]thymidine for 1 h and DNA prepared for scintillation counts or stained with propidium iodide for cell cycle analysis by flow cytometry. Overall [3H]thymidine uptake per cell was greater in mdx than control cells (mainly fibroblasts and mixed cells) and was decreased by T3 only in myoblast and mixed cultures. Cell cycle data showed that the effects of T3 originated primarily at the G0/G1 phase. There were more mdx than control myoblasts at G0/G1 without T3. After T3 treatment, more control fibroblasts than myoblasts were at G0/G1, but more mdx myoblasts than fibroblasts were at G0/G1. In the absence of T3, there were also fewer mdx than control myoblasts in S. After T3, only the proportion of mdx myoblasts in S phase was reduced. Results are consistent with distinct T3 effects on muscle regeneration in vivo and support the hypothesis that cycling and proliferation of mdx and control myoblasts are differentially modulated by T3. As control and mdx fibroblasts also showed distinct responses to T3, muscle regeneration likely occurs by a complex regulation of gene expression endogenous to specific cell types as well as interactions between cells of different lineage.

Animals↗

PubMed1994

Neurotrophic influences on corneal epithelial cells.

Innervation plays an important role in the maintenance of corneal structure and function. Neuropeptides contained in corneal nerves may be involved in these effects. This study was aimed to determine the influence of trigeminal and sympathetic neurons and of neuropeptides on proliferative activity of corneal epithelial cells in vitro. Corneal epithelial cells from adult rabbits were cultured alone or cocultured either with sensory neurons from the trigeminal ganglion or sympathetic cells from the superior cervical ganglion of newborn rabbits. Neurons and corneal epithelial cells shared the culture medium but lacked physical contact. After 2 or 7 days of coculture, or after treatment with substance P (SP) and/or calcitonin gene-related peptide (CGRP), the number of corneal cells was determined with a haemocytometer, and the incorporation of 3H-thymidine into corneal epithelial cells analysed by scintillation counting. Cell number and 3H-thymidine incorporation increased 3 and 2.5 times respectively (P < 0.01; P < 0.05), after 2 days of coculture of corneal epithelial cells with trigeminal neurons but this increase was reversed after 7 days of coculture. Sympathetic neurons had a stimulating effect on corneal epithelial cell proliferation that was apparent after 7 days of coculture (P < 0.01). A single administration of SP (10 microM) produced an increase in 3H-thymidine incorporation after 1 hr and an enhanced number of corneal epithelial cells 24 hr later. The same effect could be obtained by repeated administration of lower concentrations of SP (0.1 microM, six times over a 24 hr period). CGRP (1 microM) inhibited mitotic activity of corneal cells 12 hr after treatment. The effect could be reversed by simultaneous administration of SP (0.1 microM). These results indicate that trigeminal and sympathetic neurons modulate proliferation and perhaps differentiation of corneal epithelium cells in vitro. A stimulating effect was also obtained with SP while mitotic activity was inhibited by CGRP, thus suggesting that peptides contained in sensory nerve terminals may contribute to neural influences on epithelial cell proliferation.

Animals↗

PubMed1993

Time- and dose-dependent 45Ca2+ accumulation in rat striatum and substantia nigra after an intrastriatal injection of quinolinic acid.

To evaluate the use of cerebral 45Ca accumulation as an index for neurotoxic brain damage, the dose and time dependency of regional 45Ca accumulation in the rat brain following an unilateral injection of quinolinic acid (QUIN) into the striatum was investigated. Accumulation of radioactivity was assessed 6 h or 1, 2, 7, 21, 42, and 84 days after QUIN and 6 h or 1 day after ip 45CaCl2 injection using liquid scintillation counting of dissected brain tissues and semiquantitative autoradiography of brain sections. Dissected striata were also used for assay of glutamic acid decarboxylase (GAD) activity and after autoradiography brain sections were stained with thionine or for cholinesterase. One week after QUIN (0-50 micrograms) a dose-dependent increase in 45Ca accumulation in the injected striatum and the ipsilateral substantia nigra, but not in frontal cortex or cerebellum, was observed. In addition, 45Ca accumulation and GAD reduction in the striatum was highly significantly correlated. In the striatum 45Ca accumulated rapidly within 48 h and after this time point--by this time GAD had reached a minimum--the 45Ca content continued to increase in the lesioned striatum until Day 42. Six hours after QUIN 45Ca accumulated in the immediate vicinity of the injection site, whereas the increase 6 weeks later is primarily due to accumulation of 45Ca in striatal tissue more remote from the injection site. In the ipsilateral substantia nigra 45Ca accumulation reached a maximum 7 days after QUIN, probably reflecting delayed transneuronal death rather than degeneration of striatonigral nerve terminals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1997

Suppression of apoptosis by gonadotropin, 17beta-estradiol, and epidermal growth factor in rainbow trout preovulatory ovarian follicles.

In this study we present the first evidence for the occurrence of apoptotic cell death in ovarian follicles from teleost fish. Preovulatory ovarian follicles from mature hatchery-raised rainbow trout (Oncorhynchus mykiss) were collected and either immediately frozen in liquid nitrogen or incubated in serum-free medium at 18 degrees for 24 hr. The extent of ovarian apoptotic DNA fragmentation was determined using 3'-end labeling of DNA with [32P]dideoxy-ATP, size fractionation by agarose gel electrophoresis, and quantification of low-molecular-weight (<15 kb) DNA using autoradiography and liquid scintillation counting. The extent of apoptotic DNA fragmentation was eightfold greater in immediately frozen preovulatory follicles than in previtellogenic ovarian follicles collected from immature rainbow trout (P < 0.05), suggesting differences in the degree of apoptosis at different stages of follicular development. In preovulatory trout follicles, the extent of apoptotic DNA fragmentation was fivefold greater in follicles incubated for 24 hr. Treatment of incubated preovulatory follicles with either partially purified salmon gonadotropin SG-G100 (1 microg/ml) or epidermal growth factor (EGF; 100 ng/ml) suppressed apoptotic DNA fragmentation by 31 and 41%, respectively, in comparison to untreated incubated follicles (P < 0.01). Treatment of incubated follicles with 17beta-estradiol (1-100 ng/ml) caused a concentration-dependent suppression of apoptotic DNA fragmentation (P < 0.05). These results suggest that apoptosis is involved in teleost ovarian development and that several of the hormonal factors acting as follicle survival factors in mammalian and avian ovaries may play a similar role in teleost ovarian follicles.

Animals↗

PubMed1996

Surface Functionalization of Polyethylene Terephthalate Film and Membranes by Controlled Wet Chemistry.

Surface functionalization of polyethylene terephthalate film and track-etched microporous membranes was performed using organic synthesis at the solid-liquid interface. The hydroxyl chain ends, naturally occurring in the membranes or created by basic hydrolysis in the film, were activated by reaction with p-toluenesulfonyl chloride and then coupled to [4,5-(3)H]lysine used as a model of water-soluble bioactive molecules. The ratios of derivatization were determined by liquid scintillation counting of the radioactivity associated with the samples. The hydroxyl chain ends were further reacted with 4,4'-methylene di(phenyl isocyanate); the resulting surfaces equipped with sensitive isocyanate spacers were assayed as before using [4,5-(3)H]lysine. The ranges of derivatization were from 5 to 60 pmol of fixed amino acid per open surface unit (cm(2)). Some samples were also analyzed by X-ray photoelectron spectroscopy.

Journal Article↗