Drug-binding properties of human alpha-foetoprotein.
Ontology highlight
ABSTRACT:
SUBMITTER: Hirano K
PROVIDER: S-EPMC1152721 | biostudies-other | 1985 Oct
REPOSITORIES: biostudies-other
Similar Datasets
Project description:Rat alpha-foetoprotein (alpha-FP) strongly binds the drugs warfarin and phenylbutazone, as does albumin; however, the binding sites for the two drugs seemed to be different. This possibility and the specificity of this/these drug-binding site(s) of rat alpha-FP were investigated by competitive protein-binding experiments with a variety of drugs, representing different pharmacological groups, and biomolecules that are strongly bound by the foetal protein and that are suspected to play a specific role during foetal development. The binding mechanisms were further investigated by using comparisons between computer-derived theoretical displacement curves and experimental points in order to distinguish different possible binding models. The results indicate: that warfarin and phenylbutazone are bound at two distinct sites on rat alpha-FP and that a negative modulatory effect is exerted between the two sites; that the degree of specificity of these two drug-binding sites is different, since the warfarin-binding site appears to be specific for the binding of coumarinic and anthranilic drugs whereas that for phenylbutazone is able to bind substances of very varied chemical structure and is more hydrophobic; that the phenylbutazone-binding site is the site that binds oestrogens that thyroid hormones and, probably, fatty acids and bilirubin are bound at (an)other site(s) but exert negative modulatory effects on phenylbutazone binding. The nature of the different binding areas of rat alpha-FP is compared with that of those already proposed for albumin. The potential risks of toxicity of such interactions between drugs and/or biomolecules on foetal development are also discussed.
| S-EPMC1147300 | biostudies-other
Project description:As part of an investigation into whether alpha 1-foetoprotein (alpha 1-FP) plays the same transport role in foetal serum as albumin does in the adult, the binding properties of both proteins were compared with respect to the binding of a series of compounds known to be bound by albumin's specific drug-binding sites. The binding of warfarin, phenylbutazone, azapropazone, diazepam, digitoxin and cholic acid by rat alpha 1-FP and serum albumin was studied by equilibrium dialysis at 4 degrees C. Rat alpha 1-FP was shown to have neither albumin's high-affinity site II (diazepam as marker) nor its site III (digitoxin and cholic acid as markers). High-affinity binding by alpha 1-FP was found for the specific markers (warfarin, phenylbutazone, azapropazone) of albumin's drug-binding site I. However, instead of albumin's one high-affinity site/molecule, a mean value of 0.5 site/molecule was obtained with rat alpha 1-FP. Charcoal treatment at neutral pH of rat serum albumin did not affect its measured binding properties, but treatment of the alpha 1-FP led to an increased affinity for warfarin, phenylbutazone and azapropazone without a change in the measured number of sites, indicating competition for binding at this site by (an) endogenous ligand(s). These results are discussed in terms of the structures of the two proteins and with respect to the physiological implications of the differences found.
| S-EPMC1144051 | biostudies-other
Project description:1. Rat alpha-foetoprotein, an oestrogen-binding foetal globulin, was isolated in large quantities from amniotic fluid and serum by preparative electrophoresis on polyacrylamide slab gels or by chromatography on an immunoadsorbent column. Subsequently the two electrophoretic forms of this protein were separated by electrophoresis on the same medium. 2. Both forms were found to show identical binding with oestradiol. From the extrinsic fluorescence of the bound dye 8-anilinonaphthalene-1-sulphonic acid it was shown that the polarity of the binding site is practically identical for both forms. One residue of tryptophan was determined for both forms. The two electrophoretic variants display the same amount of secondary structure as demonstrated by circular dichroism. 3. The affinity of total alpha-foetoprotein for oestradiol as a function of pH was studied by using a Sephadex G-25 gel-equilibration method. Maximal binding occurred at pH8.5. Only a fractional number of binding sites per molecule could be measured at pH7.4, whereas at higher pH the number of sites was very close to unity. There was no significant effect of pH on the value of the association constant (K(a)=4.3x10(7)+/-1.2x10(7)m(-1)). 4. Displacement experiments of bound labelled oestradiol with various steroids have permitted investigation of the specificity of alpha-foetoprotein. This foetal globulin binds rather strongly compounds that display the rigid structure of the oestratriene skeleton (oestradiol, oestrone). Diminished binding for diethylstilboestrol and a diethylstilboestrol affinity label was observed. No binding was measured with a more flexible structure such as hexoestrol [4,4'-(1,2-diethylethane-1,2-diyl)bisphenol]. 5. Chemical modification of cysteine residues of alpha-foetoprotein with two alkylating reagents [iodoacetic acid and 8-[N-(iodoacetylaminoethyl)amino]naphthalene-1-sulphonic acid] has very little effect on the oestrogen binding. It is suggested that the oestrogen-binding site does not contain a cysteine residue. From the kinetics of alkylation and from the fluorescence properties of the chemically bound thiol reagent 8-[N-(iodoacetylaminoethyl)amino]naphthalene-1-sulphonic acid], it was demonstrated that the very-slow-reacting thiol group is probably located in a non-polar region of the molecule.
| S-EPMC1186042 | biostudies-other
Project description:The participation in drug binding of the lone tryptophan residue of rat alpha-foetoprotein (alpha-FP) and serum albumin, the two main transport proteins of foetal serum, has been studied by two different techniques. Firstly, the effect on phenylbutazone and warfarin binding of the chemical derivatization of the lone tryptophan residue of both proteins by 2-nitrophenylsulphonyl chloride (NPS) was studied. Secondly, the effect of phenylbutazone binding on the intrinsic fluorescence of the tryptophan residue of rat alpha-FP and albumin was investigated. The specific modification of the proteins by NPS did not affect the binding of warfarin by rat alpha-FP and albumin, but greatly decreased the affinity of the high-affinity sites of rat alpha-FP for phenylbutazone, though the numbers of these sites were not significantly changed. However, for albumin a similar decrease in the affinity constant appeared to be due to the reaction conditions. The spectrofluorimetric studies showed that the lone tryptophan residue of alpha-FP and albumin was quenched by phenylbutazone binding, and the quenching paralleled the fractional saturation of the high-affinity site only in the case of albumin. The effect of phenylbutazone binding on the intrinsic fluorescence of rat alpha-FP indicated that the lone tryptophan residue of this foetal protein is not in the same molecular environment as that of albumin, not participating directly in the high-affinity site for phenylbutazone, and the effect may be via some induced conformational change in rat alpha-FP. These results also confirm our previous suggestion that the high-affinity sites for phenylbutazone and warfarin are different on the rat alpha-FP molecule. The results seem to indicate that this is also the case for albumin, but confirmation is necessary.
| S-EPMC1147956 | biostudies-other
Project description:Two structurally-related members of the lysosomal mannosidase family, the broad substrate specificity enzyme human lysosomal alpha-mannosidase (hLM, MAN2B1) and the human core alpha-1, 6-specific mannosidase (hEpman, MAN2B2) act in a complementary fashion on different glycosidic linkages, to effect glycan degradation in the lysosome. We have successfully expressed these enzymes in Drosophila S2 cells and functionally characterized them. hLM and hEpman were significantly inhibited by the class II alpha-mannosidase inhibitors, swainsonine and mannostatin A. We show that three pyrrolidine-based compounds designed for selective inhibition of Golgi alpha-mannosidase II (GMII) exhibited varying degrees of inhibition for hLM and hEpman. While these compounds inhibited hLM and GMII similarly, they inhibited hEpman to a lesser extent. Further, the two lysosomal alpha-mannosidases also show differential metal dependency properties. This has led us to propose a secondary metal binding site in hEpman. These results set the stage for the development of selective inhibitors to members of the GH38 family, and, henceforth, the further investigation of their physiological roles.
| S-EPMC2788279 | biostudies-literature
Project description:The binding of bilirubin to rat-alpha-foetoprotein has been measured by changes in the absorption spectrum and by the appearance of two intense circular-dichroism bands. Furthermore binding of this bile pigment has been demonstrated by a decrease of its enzymic oxidation rate and by competition experiments with bovine serum albumin-agarose. The binding parameters have been determined as follows: n = 1.0 mol bound/mol of protein and Ka = 2.9 X 10(6) M-1. Competition of oestradiol for the bilirubin-binding site has not been established.
| S-EPMC1186681 | biostudies-other
Project description:The temporal accumulation of the electrophoretic components of mouse alpha-foetoprotein in foetal plasma and amniotic fluid is reported. To explain the progressive appearance of the sialylated alpha-foetoproteins, the activity of sialyltransferase in foetal liver and yolk sac was measured. These results indicate that the increase in sialyltransferase activity in these tissues is responsible for the increased sialylation of alpha-foetoprotein.
| S-EPMC1177877 | biostudies-other
Project description:Purified Candida albicans sterol 14-? demethylase (CaCYP51) bound the CYP51 substrates lanosterol and eburicol, producing type I binding spectra with K(s) values of 11 and 25 ?M, respectively, and a K(m) value of 6 ?M for lanosterol. Azole binding to CaCYP51 was "tight" with both the type II spectral intensity (?A(max)) and the azole concentration required to obtain a half-?A(max) being proportional to the CaCYP51 concentration. Tight binding of fluconazole and itraconazole was confirmed by 50% inhibitory concentration determinations from CYP51 reconstitution assays. CaCYP51 had similar affinities for clotrimazole, econazole, itraconazole, ketoconazole, miconazole, and voriconazole, with K(d) values of 10 to 26 ?M under oxidative conditions, compared with 47 ?M for fluconazole. The affinities of CaCYP51 for fluconazole and itraconazole appeared to be 4- and 2-fold lower based on CO displacement studies than those when using direct ligand binding under oxidative conditions. Econazole and miconazole were most readily displaced by carbon monoxide, followed by clotrimazole, ketoconazole, and fluconazole, and then voriconazole (7.8 pmol min(-1)), but itraconzole could not be displaced by carbon monoxide. This work reports in depth the characterization of the azole binding properties of wild-type C. albicans CYP51, including that of voriconazole, and will contribute to effective screening of new therapeutic azole antifungal agents. Preliminary comparative studies with the I471T CaCYP51 protein suggested that fluconazole resistance conferred by this mutation was through a combination of increased turnover, increased affinity for substrate, and a reduced affinity for fluconazole in the presence of substrate, allowing the enzyme to remain functionally active, albeit at reduced velocity, at higher fluconazole concentrations.
| S-EPMC2944560 | biostudies-literature
Project description:The binding affinity is determined by the Gibbs energy of binding (?G) which is the sum of enthalpic (?H) and entropic (-T?S) contributions. Because the enthalpy and entropy contribute in an additive way to the binding energy, the same binding affinity can be achieved by many different combinations of enthalpic and entropic contributions; however, do compounds with similar binding affinities but different thermodynamic signatures (i.e., different ?H, -T?S combinations) exhibit the same functional effects? Are there characteristics of compounds that can be modulated by modifying their thermodynamic signatures? In this paper, we consider the minimization of unwanted conformational effects arising during the development of CD4/gp120 inhibitors, a new class of HIV-1 cell entry inhibitors. Competitive inhibitors of protein/protein interactions run the risk of triggering the very same signals that they are supposed to inhibit. Here, we show that for CD4/gp120 inhibitors, the magnitude of those unwanted effects is related to the proportion in which the enthalpy and entropy changes contribute to the binding affinity. The thermodynamic optimization plot (TOP) previously proposed to optimize binding affinity can also be used to obtain appropriate enthalpy/entropy combinations for drug candidates.
| S-EPMC3079564 | biostudies-literature
Project description:Secretion and glycosylation of alpha-foetoprotein (AFP) by mouse yolk sac were studied by using yolk-sac explants cultured in vitro. Yolk-sac explants rapidly incorporated [35S]methionine into AFP, whereas radioactively labelled AFP was not found in the medium until 30 min after incubation was initiated. Electrophoretic analysis revealed that microheterogeneity of AFP synthesized in explants increased in parallel with the gestational age of the yolk sacs. The change in microheterogeneity was noted by the formation of increasingly acidic forms. Only the most acidic forms of AFP were found to be present in the medium on each gestational day studied. Tunicamycin reduced the incorporation of glucosamine into AFP with a concomitant decrease in molecular weight and microheterogeneity. However, the relative amount of AFP released into the medium was not altered by the presence of tunicamycin. The presence of under-glycosylated AFP in the medium indicates that glycosylation of AFP is not essential for its secretion from the yolk sac. In light of these and previous findings, it is suggested that the glycosylation of AFP may be important for the turnover of this glycoprotein in serum.
| S-EPMC1152049 | biostudies-other