Role of avidin and other biotin-binding proteins in the deposition and distribution of biotin in chicken eggs. Discovery of a new biotin-binding protein.

In addition to the previously characterized egg-yolk biotin-binding protein (BBP-I), we have discovered another BBP (BBP-II) in the plasma and yolk from laying hens. BBP-I is stable to 65 degrees C, whereas BBP-II is stable to 45 degrees C. Both proteins are normally saturated with biotin and together they account for most, if not all, of the biotin in hen plasma and yolk, except in hens fed excessive amounts of biotin (greater than 1 mg of biotin/kg of feed). The maximal production of BBP-I is attained at lower levels of dietary biotin (approximately 50 micrograms/kg) than for BBP-II (approximately 250 micrograms/kg); however, the maximal production of BBP-II is severalfold greater than for BBP-I. Consequently, as dietary biotin increases, the ratio of BBP-II to BBP-I increases and becomes constant at dietary intakes of biotin above 250 micrograms/kg. The observation that the amounts of these proteins are limited by biotin in the normal dietary range (less than 250 micrograms/kg) suggests that biotin is required for the synthesis, secretion or stability of these proteins. Although both plasma vitamin-protein complexes are transported to the oocyte and concentrated in the yolk, BBP-II is transferred more efficiently. Thus biotin deposition in the yolk is a function of the amounts and relative concentrations of the two proteins. Dietary biotin above 250 micrograms/kg exceeds the transport capacity of BBP-I and BBP-II in the plasma; however, unbound biotin does not accumulate. Rather it is efficiently scavenged by avidin in the oviduct and transferred to the egg albumen. Only when avidin becomes saturated at high dietary intake does free or weakly bound biotin accumulate in plasma and yolk. The synthesis of avidin is independent of dietary biotin. Small amounts of BBPs with the heat-stability of avidin or BBP-I respectively are present in the plasma of adult males or immature chickens. BBP-II, the major BBP in the plasma and yolk of laying hens, was not detected in the plasma of non-laying chickens.     

Biotin-binding protein from chicken egg yolk. Assay and relationship to egg-white avidin.

1. Biotin in chicken egg yolk is non-covalently bound to a specific protein that comprises 0.03% of the total yolk protein (0.8 mg/yolk). This biotin-binding protein is not detectable by the normal avidin assay owing to the biotin being tightly bound. Exchange of [14C]biotin for bound biotin at 65 degrees C is the basis of an assay for this protein. 2. Biotin-binding protein from egg yolk is distinguishable from egg-white avidin on Sephadex G-100 gel filtration, although the sizes of the two proteins appear quite similar. 3. Biotin-binding protein is denatured at a lower temperature and freely exchanges biotin at lower temperatures than does avidin. 4. The biotin-binding protein in egg yolk is postulated to be responsible for the deposition of biotin in egg yolk. D-[carboxyl-14C]Biotin injected into laying hens rapidly appears in the egg bound to yolk biotin-binding protein and avidin. Over 60% of the radioactivity is eventually deposited in eggs. The kinetics of biotin deposition in the egg suggests a 25 day half-life for an intracellular biotinyl-coenzyme pool in the laying hen.     

Availability of avidin-bound biotin to the chicken embryo.

Avidin, an exceptionally stable protein in egg white, binds the vitamin biotin with very high affinity and can induce biotin deficiency when fed to animals. To determine if biotin bound to avidin is available to the chicken embryo, the fate of [3H]biotin complexed to avidin was monitored during embryonic development. The majority (greater than 85%) of the [3H]biotin was extraembryonic until the day before hatching, when embryos swallow egg white and withdraw the yolk sac into their abdomen. Thus, biotin in the egg white of chicken eggs contributes little to the biotin status of the chick prior to hatching. After hatching, much of the [3H]biotin was assimilated. About 30% of the total was found in the liver and kidneys by 4 days of age. The biotin in liver was associated with large proteins and not with avidin. In a separate experiment, biotin injected into the egg white of biotin-deficient eggs failed to increase embryonic development or hatchability. Both experiments suggest that biotin in egg yolk is the primary and virtually sole source of biotin for the chicken embryo.     

A spectrophotometric assay for nanogram quantities of biotin and avidin

Parameters and conditions of an enzyme based assay for biotin and avidin are presented. Biotinylated glucose-6-phosphate dehydrogenase when complexed with avidin becomes inactivated. Thus it was possible to construct a competitive assay system for biotin. The assay is sensitive between 100-500 ng/ml and could detect as little as 10 ng in 0.1 ml with a between run error of 2.4%. It requires a 60 min incubation at 21 degrees C and 5 min to assay. The avidin assay, based on the degree of inactivation of biotinylated-glucose-6-phosphate dehydrogenase in relation to the concentration of avidin, could detect as little as 0.25 ng in 0.1 ml or 2.5 ng/ml with an assay time of 10 min with a between run error of 3.9%. Both assays are rapid with significant improvements over other non-isotopic methods in sensitivity and comparable to radioisotopic methods in sensitivity with the added advantage of ease of method.     

Extension of the single amino acid chelate concept (SAAC) to bifunctional biotin analogues for complexation of the M(CO)3(+1) Core (M = Tc and Re): syntheses, characterization, biotinidase stability, and avidin binding

Biotin and avidin form one of the most stable complexes known (K(D) = 10(-15) M(-1)) making this pairing attractive for a variety of biomedical applications including targeted radiotherapy. In this application, one of the pair is attached to a targeting molecule, while the other is subsequently used to deliver a radionuclide for imaging and/or therapeutic applications. Recently, we reported a new single amino acid chelate (SAAC) capable of forming stable complexes with Tc(CO)3 or Re(CO)3 cores. We describe here the application of SAAC analogues for the development of a series of novel radiolabeled biotin derivatives capable of forming robust complexes with both Tc and Re. Compounds were prepared through varying modification of the free carboxylic acid group of biotin. Each 99mTc complex of SAAC-biotin was studied for their ability to bind avidin, susceptibility to biotinidase, and specificity for avidin in an in vivo avidin-containing tumor model. The radiochemical stability of the 99mTc(CO)3 complexes was also investigated by challenging each 99mTc-complex with large molar excesses of cysteine and histidine at elevated temperature. All compounds were radiochemically stable for greater than 24 h at elevated temperature in the presence of histidine and cysteine. Both [99mTc(CO)3(L6)]+1 [TcL6; L6 = biotinylamidopropyl-N,N-(dipicolyl)amine] and [99mTc(CO)3(L12a)]+1 (TcL12; L12 = N,N-(dipicolyl)biotinamido-Boc-lysine; TcL12a; L12a = N,N-(dipicolyl)biotinamide-lysine) readily bound to avidin whereas [99mTc(CO)3(L9)]+1 [TcL9; L9 = N,N-(dipicolyl)biotinamine] demonstrated minimal specific binding. TcL6 and TcL9 were resistant to biotinidase cleavage, while TcL12a, which contains a lysine linkage, was rapidly cleaved. The highest uptake in an in vivo avidin tumor model was exhibited by TcL6, followed by TcL9 and TcL12a, respectively. This is likely the result of both intact binding to avidin and resistance to circulating biotinidase. Ligand L6 is the first SAAC analogue of biotin to demonstrate potential as a radiolabeled targeting vector of biotin capable of forming robust radiochemical complexes with both 99mTc and rhenium radionuclides. Computational simulations were performed to assess biotin-derivative accommodation within the binding site of the avidin. These calculations predict that deformation of the surface domain of the binding pocket can occur to accommodate the transition metal-biotin derivatives with negligible changes to the inner-beta-barrel, the region most responsible for binding and retaining biotin and its derivatives. The biological activity and biodistribution of the technetium complexes TcL6, TcL9, and TcL12a were examined in an avidin tumor model. In the avidin bead tumor localization model, TcL6 demonstrated the most favorable localization with a 7:1 ratio of avidin bead implanted muscle versus normal muscle, while TcL9 exhibited a 2:1 ratio. However, TcL9 displayed no specificity for avidin.     

A radioimmunoassay for chicken avidin. Comparison with a [14C]biotin-binding method.

A double-antibody solid-phase radioimmunoassay for chicken avidin is reported. Avidin was labelled with 125I by the chloramine-T method. The bound and free avidin were separated with a second antibody bound to a solid matrix. In the logit-log scale the standard curve was linear from 1-2 to 100-200ng of avidin/ml. Cross-reaction of ovalbumin was less than 0.015%. Saturation of biotin-binding sites of avidin with an excess of biotin decreased radioimmunoassay values by about 15%. Recovery studies indicated that avidin can be assayed from all chicken tissues studied with radioimmunoassay, whereas the [14C]biotin/bentonite method gave poor recoveries for avidin in the liver and kidney. Radioimmunoassay and the [14C]biotin/bentonite method gave similar concentrations for oviduct avidin.     

Regulation of Biotin Transport in Saccharomyces cerevisiae

The metabolic control of biotin transport in Saccharomyces cerevisiae was investigated. Nonproliferating cells harvested from cultures grown in excess biotin (25 ng/ml) took up small amounts of biotin, whereas cells grown in biotin-sufficient medium (0.25 ng/ml) accumulated large amounts of the vitamin. Transport was inhibited maximally in cells grown in medium containing 9 ng (or more) of biotin per ml. When avidin was added to biotin-excess cultures, the cells developed the ability to take up large amounts of biotin. Boiled avidin was without effect, as was treatment of cells with avidin in buffer. Avidin did not relieve transport inhibition when added to biotin-excess cultures treated with cycloheximide, suggesting that protein synthesis was required for cells to develop the capacity to take up biotin after removal of extracellular vitamin by avidin. Cycloheximide did not inhibit the activity of the preformed transport system in biotin-sufficient cells. The presence of high intracellular free biotin pools did not inhibit the activity of the transport system. The characteristics of transport in biotin-excess cells (absence of temperature or pH dependence, no stimulation by glucose, absence of iodoacetate inhibition, independence of uptake on cell concentration, and nonsaturation kinetics) indicated that biotin entered these cells by diffusion. The results suggest that the synthesis of the biotin transport system in S. cerevisiae may be repressed during growth in medium containing high concentrations of biotin.     

Regulation of avidin accumulation by prostaglandins in chick oviduct culture

Regulation of avidin accumulation by prostaglandins (PGs) and their inhibitors was studied in chick oviduct organ culture. Avidin was induced neither by progesterone nor PGF2 alpha in the oviduct of immature chicks. By progesterone and PGs, a high avidin synthesis was induced when the chicks received diethylstilbestrol (DES) for 7 days. Enhanced avidin production was observed by PGF2 alpha, PGE1 and PGE2, whereas PGA2 and PGB2 had a slight inhibitory effect and PGA1 and PGB1 had no effect on avidin production. PGF2 alpha was most effective at a concentration of 10-20 micrograms/ml. The effects of progesterone and PGF2 alpha were not additive. Mefenamic acid, at concentrations of 40 and 60 micrograms/ml, inhibited 50 and 85%, respectively, of the avidin synthesis induced by progesterone, whereas the inhibition of the total protein synthesis was only 20%, and this only by the higher concentration of the drug. Tolfenamic and meclofenamic acid were also inhibitory in the case of progestin-induced avidin synthesis. These studies indicate that the PGs (F2 alpha, E1 and E2) might be involved in the avidin induction in the chick differentiated oviduct. The specific inhibition of the progesterone-dependent avidin synthesis by the PG inhibitors suggests that PGs may be connected with the progesterone action in the oviduct. We propose that the avidin synthesis by the chick oviduct might be considered as a model system for studying PG effects on the synthesis of a specific protein.     

A chip-based method for studying the effects of exogenous proteins on neuronal axons

It has been reported that the activity of protein improved when it was adsorbed inside the pores of mesoporous silica (MPS). The current study investigated the activity of immobilized avidin to the biotin on MPS with various pore sizes (diameter=2.4-45.0 nm). The binding amount of immobilized avidin to biotin is 123 to 160 ng biotin/10 μg avidin on 2.7- to 5.4-nm pore MPS, but that on 12- to 45-nm pore MPS was markedly decreased (33-42 ng biotin/10 μg). Moreover, the binding amount was approximately 2- and 3-fold higher on the glycidoxypropyl (Gly)-functionalized 5.4- and 45-nm pore MPS in comparison with methyl (Me)-functionalized 5.4- and 45-nm pore MPS, respectively. Furthermore, avidin immobilized in native and Gly-grafted 45-nm pore MPS retained more than 70% and 50% binding activity to biotin, respectively, after incubating at 90°C for 3 h. In contrast, the activity was greatly reduced in the native and Gly-grafted 5.4-nm pore MPS under the same conditions (<36.9%). The immobilization also protected against effects of 0.01 M HCl and 50% MeOH; all of immobilized avidin proteins showed high activity (>50%) with biotin compared with that observed with free avidin (MeOH [<18.2%] and HCl [<32.7%]).     

A sensitive enzyme assay for biotin, avidin, and streptavidin

Reciprocal enzyme assays are described for the vitamin biotin and for the biotin-binding proteins avidin and streptavidin. The assays are based on the following steps: (a) biotinylated bovine serum albumin is adsorbed onto microtiter plates; (b) streptavidin (or avidin) is bound to the biotin-coated plates; (c) biotinylated enzyme (in this case alkaline phosphatase) is then interacted with the free biotin-binding sites on the immobilized protein. For biotin assay, competition between the free vitamin and the biotinylated enzyme is carried out between steps (b) and (c). The method takes advantage of the four biotin-binding sites which characterize both avidin and streptavidin. The method is extremely versatile and accurate over a concentration range exceeding three orders of magnitude. The lower limits of detection are approximately 2 pg/ml (0.2 pg/sample) for biotin and less than 100 ng/ml (10 ng/sample) for either avidin or streptavidin.     

Colorimetric competitive inhibition method for the quantification of avidin, streptavidin and biotin.

A colorimetric competitive inhibition assay for avidin, streptavidin and biotin was developed. The method for avidin or streptavidin was based on the competitive binding between avidin or streptavidin and a streptavidin-enzyme conjugate for biotinylated dextrin immobilized on the surface of a microtitre plate. For biotin quantitation the competition is between free biotin and the immobilized biotin for the streptavidin-enzyme conjugate. The limits of detection which was determined as the concentration of competitor required to give 90% of maximal absorbency (100% inhibition) was approximately 20 ng/100 microl per assay for avidin and streptavidin and 0.4 pg/100 microl per assay for biotin. The methods are simple, rapid, highly sensitive and adaptable to high throughput analysis.     

Characterization of fully active biotinylated parathyroid hormone analogs. Application to fluorescence-activated cell sorting of parathyroid hormone receptor bearing cells

[Nle8,18,Tyr34]bPTH-(1-34)amide (NlePTH) was biotinylated using sulfosuccinimidyl 6-(biotinamido)hexanoate, in dimethyl sulfoxide, and the multiple resulting peptides peaks were separated by reverse-phase high performance liquid chromatography. Their biological activities were compared with those of NlePTH, the parent compound, in radioreceptor and cAMP accumulation bioassays using rat osteosarcoma 17/2.8 cells; the earliest two eluting products, bioPTH 1 and 2, were equipotent, a third, bioPTH 3, was only 10% as potent, and the remaining, later eluting derivatives all were less than 0.1% as active. Competitive avidin binding assays using [3H]biotin suggested that bioPTH 1 and 2 had a single biotin congener per molecule, while bioPTH 3 contained two biotin residues. Upon Edman degradation, bioPTH 1 contained biotin on the lysine at position 13 of NlePTH; bioPTH 2's biotin was on the lysine at position 26 (or 27) and bioPTH 3 had biotins on lysines at both positions 13 and 26 (or 27). Avidin tagged with 125I, peroxidase, or fluorescein isothiocyanate was detected on bone-derived cells which had been incubated initially with bioPTH 2 (1, 10, and 100 nM) for 4 h, but not when NlePTH (1 microM) was added with bioPTH 2. A fluorescence-activated cell sorter detected a symmetrical shift in fluorescence of bone-derived cells incubated with 10 nM of bioPTH 2 and 10 micrograms/ml fluorescein isothiocyanate-avidin. Addition of a 30-fold molar excess of NlePTH, or omission of bioPTH 2, completely reversed this fluorescence shift, and no shift in fluorescence was seen with cells lacking PTH receptors. This fully active, high affinity biotinylated PTH-derivative should prove useful in the study of PTH receptor-bearing cells.     

Insecticidal activity of recombinant avidin produced in yeast

An expression construct encoding chicken (Gallus gallus) avidin was assembled from amplified fragments of genomic DNA. Recombinant, functional avidin was produced in Pichia pastoris, with yields of up to 80 mg/l of culture supernatant. The recombinant avidin had similar insecticidal activity to egg white avidin when assayed against larvae of a lepidopteran crop pest, cabbage moth (Mamestra brassicae), causing >90% reduction in growth and 100% mortality when fed in optimised diets at levels of 1.5 μM and 15 μM (100 ppm and 1000 ppm wet weight of recombinant protein). The recombinant protein was also highly toxic to a hemipteran pest, the pea aphid (Acyrthosiphon pisum), when fed in liquid artificial diet, causing 100% mortality after 4 days when present at concentrations ≥3.8 μM (0.25 mg/ml, 250 ppm). Mortality was dose-dependent, with an estimated LC₅₀ of 2.1 μM. Toxicity to A. pisum was prevented by biotin supplementation of diet. In contrast, avidin had no significant effects on the survival of cereal aphid (Sitobion avenae) at concentrations up to 30 μM in liquid diet. Analysis of genomic DNA showed that symbionts from both aphid species lack the ability to synthesise biotin de novo. Cereal aphids appear to be less sensitive to recombinant avidin in the diet through proteolysis of the ingested protein, which would allow recovery of bound biotin.     

Insecticidal activity of avidin combined with genetically engineered and traditional host plant resistance against Colorado potato beetle (Coleoptera: Chrysomelidae) larvae

Colorado potato beetle, Leptinotarsa decemlineata (Say), is a destructive pest of potato, Solanum tuberosum (L.), in North America. It is renowned for adapting to insecticides. With the arsenal of effective insecticides decreasing, it is important to consider alternative forms of control. Biotin is an essential coenzyme for insect growth and development. Avidin is a protein found in chicken egg that sequesters biotin and has shown insecticidal properties against a range of insect. We assessed the effectiveness of avidin against the Colorado potato beetle neonates in a no-choice detached leaf bioassay at 0, 17, 34, 51, 102, and 204 microg avidin/ml over 12 d. The LC50 was 136 microg avidin/ml (108-188 95% CL). The combined effects of avidin (136 microg avidin/ml) with Bt-Cry3A or leptines were evaluated with neonates and third instars over 12 and 6 d, respectively. Three potato lines were used: susceptible line, a line engineered to express Cry3A from Bacillus thuringiensis, and a line expressing the natural resistance factor leptines. The addition of avidin at the LC50 concentration significantly reduced consumption by neonates, but it did not affect consumption by third instars feeding on the susceptible line and the leptine line. Survival of neonates feeding on the susceptible line with avidin was significantly reduced compared with the susceptible line. Survival of third instars on the Bt-Cry3A with avidin was significantly reduced after 3 d compared with survival on the Bt-Cry3A, suggesting the addition of avidin may increase susceptibility to Bt-Cry3A.     

Disintegration of layer-by-layer assemblies composed of 2-iminobiotin-labeled poly(ethyleneimine) and avidin

A layer-by-layer thin film composed of avidin and 2-iminobiotin-labeled poly(ethyleneimine) (ib-PEI) was prepared and their sensitivity to the environmental pH and biotin was studied. The avidin/ib-PEI multilayer assemblies were stable at pH 8-12, whereas the assemblies were decomposed at pH 5-6 due to the low affinity of the protonated iminobiotin residue to avidin. The avidin/ib-PEI assemblies can be disintegrated upon addition of biotin and analogues in the solution as a result of the preferential binding of biotin or analogues to the binding site of avidin. The decomposition rate was arbitrarily controlled by changing the type of stimulant (biotin or analogues) and its concentration. The avidin/ib-PEI assemblies were disintegrated rapidly by the addition of biotin or desthiobiotin, whereas the rate of decomposition was rather slow upon addition of lipoic acid or 2-(4'-hydroxyphenylazo)benzoic acid. The present system may be useful for constructing the stimuli-sensitive devices that can release drug or other functional molecules.     

Effect of Ketoconazole,a Cytochrome P450 Inhibitor,on the Efficacy of Quinine and Halofantrine against Schistosoma mansoni in Mice

The fear that schistosomes will become resistant to praziquantel (PZQ) motivates the search for alternatives to treat schistosomiasis. The antimalarials quinine (QN) and halofantrine (HF) possess moderate antischistosomal properties. The major metabolic pathway of QN and HF is through cytochrome P450 (CYP) 3A4. Accordingly, this study investigates the effects of CYP3A4 inhibitor, ketoconazole (KTZ), on the antischistosomal potential of these quinolines against Schistosoma mansoni infection by evaluating parasitological, histopathological, and biochemical parameters. Mice were classified into 7 groups: uninfected untreated (I), infected untreated (II), infected treated orally with PZQ (1,000 mg/kg) (III), QN (400 mg/kg) (IV), KTZ (10 mg/kg)+QN as group IV (V), HF (400 mg/kg) (VI), and KTZ (as group V)+HF (as group VI) (VII). KTZ plus QN or HF produced more inhibition (P<0.05) in hepatic CYP450 (85.7% and 83.8%) and CYT b5 (75.5% and 73.5%) activities, respectively, than in groups treated with QN or HF alone. This was accompanied with more reduction in female (89.0% and 79.3%), total worms (81.4% and 70.3%), and eggs burden (hepatic; 83.8%, 66.0% and intestinal; 68%, 64.5%), respectively, and encountering the granulomatous reaction to parasite eggs trapped in the liver. QN and HF significantly (P<0.05) elevated malondialdehyde levels when used alone or with KTZ. Meanwhile, KTZ plus QN or HF restored serum levels of ALT, albumin, and reduced hepatic glutathione (KTZ+HF) to their control values. KTZ enhanced the therapeutic antischistosomal potential of QN and HF over each drug alone. Moreover, the effect of KTZ+QN was more evident than KTZ+HF.     

Avidin traps biotin diffusing out of chicken egg yolk

1. The unequal distribution of biotin and biotin-binding proteins between the yolk and albumen of freshly laid chicken eggs provides the potential for time-dependent redistribution of biotin that could affect egg quality, biotin availability, and hatchability. 2. Avidin-bound biotin was measured in albumen next to the shell and next to the yolk in eggs stored up to 23 days. 3. Biotin bound to biotin-binding proteins (BBP-I and BBP-II) was measured at the center and periphery of yolk from the same eggs. 4. After 11 days of storage, significant amounts of biotin from the yolk began to accumulate in the albumen adjacent to the yolk. 5. This transfer is attributed to a change in the vitelline membrane that permits diffusion of biotin, not BBP-I or BBP-II, out of the yolk. 6. The dynamics of this phenomenon suggest that in addition to its antimicrobial role, avidin may be involved in the utilization of biotin by the chick embryo.     

Radiosynthesis, biodistribution and micro-SPECT imaging study of dendrimer-avidin conjugate

Partially acetylated generation five polyamidoamine (PAMAM) dendrimer (G5-Ac) was reacted with biotin and 2-(p-isothiocyanatobenzyl)-6-methyl-diethylenetria minepentaacetic acid (1B4M-DTPA), respectively to form the complex Bt-G5-Ac-1B4M which was further conjugated with avidin to give the conjugate Av-G5-Ac-1B4M. Then both of the conjugates were radiolabeled with technetium-99m ((99m)Tc), respectively. Their in vitro cellular uptake study shows that the conjugate of Av-G5-Ac-1B4M-(99m)Tc exhibits much higher cellular uptake in HeLa cells than that of Bt-G5-Ac-1B4M-(99m)Tc. Accordingly the following evaluation such as in vitro/in vivo stability, biodistribution and micro-SPECT imaging was observed only for the conjugate of Av-G5-Ac-1B4M-(99m)Tc.     

Chicken macrophages synthesize and secrete avidin in culture

It was previously shown that avidin, a glycoprotein secreted in vivo by chicken oviduct, is produced by cultured transformed or damaged chicken embryo fibroblasts [27]. This report demonstrates synthesis and secretion of large amounts of avidin by macrophages isolated from chicken yolk sac. Avidin was secreted to the culture medium as shown by immunoprecipitation of metabolically labeled proteins. In the culture medium of macrophages the avidin concentration (up to 47.5 +/- 0.5 microgram/mg cellular protein) exceeded, in agreement with previous findings, that of fibroblasts (up to 7.3 +/- 0.7 microgram/mg) infected with transforming retroviruses (Rous sarcoma virus, its mutants temperature sensitive for transformation and OK 10 virus). No difference between the macrophage avidin and the egg white avidin was detected by both the heat-induced [14C] biotin exchange assay and immunoblotting (subunit Mr = 15600). By immunofluorescence 10 to 20% of the cells were positive for avidin, independent of the time in culture (1-30 days). The staining pattern varied between dense or granular perinuclear and strong reticulo-granular fluorescence throughout the cytoplasm. Double staining for avidin and the Golgi region by wheat germ agglutinin showed that avidin is concentrated, and might be processed, in the Golgi complex. The production of avidin by macrophages supports a role for avidin in host defence mechanisms.     

抗生物素蛋白结合蛋白的发现及分离纯化

本文报道了在日本血吸虫感染的兔血清及日本血吸虫卵中,存在一种能与抗生物素蛋白（又称亲和素）专一性结合的蛋白质,称为抗生物素蛋白结合蛋白。该蛋白质与亲和素的结合与生物素及亲和素的糖链部分无关,并能在高ＰＨ、高浓度盐及去污剂等条件下与亲和素结合。利用ＤＥＡ－５２离子交换柱及偶联有亲和素的Ｓｅｐｈａｒｏｓｅ４Ｂ亲和层析柱,从日本血吸虫感染的兔血清中,分离纯化了该蛋白质。提纯的亲和素结合蛋白在ＳＤＳ－ＰＡ