Biomedical subjects

E I Karpyza

Publications and source records attributed to E I Karpyza.

4 recordsLinked to original sources

PubMed1993

[Simulating and inhibiting effect of individual blood serum transport proteins on thyroid hormone binding with human placental cell membrane].

Binding processes in in vitro systems modelling specific interactions between transport and receptor proteins, thyroid hormones of human placental tissue and the washing blood, have been studied. These systems included syncytiotrophoblast villous membranes, thyroxine (T4), triiodothyronine (T3) and iodothyronine-binding proteins: transthyretin, albumin, immunoglobulins (Ig) M and G, apolipoprotein A-I, and the T4-binding globulin purified from human retroplacental serum. All of the transport proteins at concentrations close to the Ka values of their complexes with thyroid hormones produced inhibitory effects on the binding of [125I]T3 or [125I]T4 to the thyroid hormone membrane receptor. The dependence of [125I]T4 membrane binding on IgM concentration in the system was characteristic of all proteins studied. In the case of T3 such dependence was unique for IgM, and included the phase of the IgM stimulatory effect (10(-11)-10(-9) M) and the phase of inhibition (10(-8)-10(-7) M). In the presence of 30 pM IgM, the concentration of the membrane T3-binding sites increased by 75% with a 2.2-fold decrease of the association constant (Ka). It was shown that IgM interacts specifically with two classes of binding sites on the plasma membranes with Ka(1) = 5.0 x 10(9) M-1, Bmax(1) = 34 fmol/mg of membrane protein and Ka(2) = 2.7 x 10(7) M-1, Bmax(2) = 2.0 pmol/mg of membrane protein. It is suggested that the stimulatory effect of IgM is caused by increases in the number of T3-binding sites on the placental villous membranes as a result of complex formation between IgM and its membrane receptor which displays an enhanced T3-binding activity.

Binding Sites↗

PubMedDate not supplied

[Characteristics of specific binding of thyroid hormones with plasma membranes of syncytiotrophoblast of human placenta].

Kinetic and equilibrium characteristics of the interaction of triiodothyronine (T3) and its structural analogues with plasmatic membranes of human placental syncytiotrophoblast were studied. The specific binding was temperature-dependent, saturable, reversible, selective and stereospecific. The following values of the binding parameters were obtained: association rate constant--1.0 x 10(10) M-1min-1, dissociation rate constant (fast phase)--2.4 x 10(-1) min-1, half-life time of the complex--2.9 min, equilibrium association constants for high- and low-affinity sites--2.0 x 10(10) M-1 and 4.8 x 10(6) M-1, respectively, concentrations of the corresponding sites--12.5 fmol and 36.0 pmol per mg of membrane protein, respectively. The affinity for membranes decreased in the following order: L = T3 greater than L = T4 greater than 3,3,5-triiodothyroacetic acid greater than 3,3,5-triiodothyropropionic acid greater than D = T3 greater than D = T4 greater than 3,5-diiodo-L-tyrosine.

Cell Membrane↗

PubMedDate not supplied

[Thyroxine-binding globulin and its molecular variant in human amniotic fluid].

Total thyroxine--binding globulin (TBGt) and its pregnancy-associated molecular variant (TBG-1) were detected by radioimmunoassay in human amniotic fluid collected at the time of delivery. TBGt purified from amniotic fluid by affinity chromatography and hydroxylapatite chromatography, displayed electrophoretic properties, immunoreactivity, a molecular mass, affinity for thyroxine and TBG-1 content identical to those of pure TBGt from human pregnancy serum. The concentrations of TBGt and TBG-1 in maternal venous blood serum were 49 +/- 7 mg/ml and 3.8 +/- 1.3 mg/ml (n = 23), respectively, and those in amniotic fluid were 2.0 +/- 0.5 mg/ml and 0.19 +/- 0.12 mg/ml (n = 30), respectively. The analysis of paired samples showed that the serum and amniotic fluid TBGt levels closely correlated (r = 0.91), whereas the correlation between the respective TBG-1 levels was poor (r = 0.63). The TBG-1/TBGt ratio in amniotic fluid was 20% higher than that in serum. These findings suggested a maternal origin of the most of the amniotic fluid TBG which may possibly enter amniotic fluid by passive diffusion through fetal membranes. An alternative mechanism can exist for TBG-1 transfer from maternal serum to amniotic fluid. It corresponds to a special role that TBG-1 may play in the fetoplacental system.

Amniotic Fluid↗

PubMedDate not supplied

[Blood levels of molecular variants of human thyroxine-binding globulin].

The concentrations of the molecular variant of the thyroxine-binding globulin (TBG-1) and total TBG were measured in normal human sera (male and female), venous blood sera at various stages of normal pregnancy as well as in matched samples of retroplacental and venous sera of mothers and in cord sera of their newborns. It was shown that TBG-1 appeared on the 6th-11th week of pregnancy and its level increased up to the delivery. A TBG-1 portion in the total TBG content increased from 2.0% in the 3rd month of pregnancy to 8.8% in the last month. After delivery TBG-1 and TBG levels decreased on the first day from 3.82 +/- 0.52 micrograms/ml to 2.52 +/- 0.86 micrograms/ml (P less than 0.01) and from 43.3 +/- 7.2 micrograms/ml to 37.8 +/- 9.6 micrograms/ml (P less than 0.01), respectively. However on the 5th day a decrease in TBG-1 and TBG concentrations were not observed. TBG-1 was undetectable in normal adult and cord sera. TBG-1 concentrations in matched retroplacental and venous sera at term were similar. These results suggested that TBG-1 was related to pregnancy-associated proteins rather than to proteins of fetal or placental origin.

Adult↗