Nuclear matrix-associated NMN adenylyltransferase activity in human placenta.

This paper presents data about the presence of the NMN adenylyltransferase at the nuclear matrix level of human placenta nuclei. It was found that 40-45% of the activity (depending on the extraction procedure) referred to the total nuclear NMN adenylyltransferase was tightly associated with this subnuclear compartment. The matrices purified by two different procedures exhibited DNA, RNA and protein contents comparable with those described in literature. Extensive digestion of human placenta nuclei with DNase I was not able to solubilize the NMN adenylyltransferase activity. Therefore, the data we present are consistent with the conclusion that a part of the total nuclear NMN adenylyltransferase is associated with the nuclear matrix.     

Keratinocyte growth-promoting activity from human placenta

Extracts of term human placenta were tested for enhancement of proliferative growth of primary cultures of human keratinocytes. Saline extracts or supernatants from homogenates were dialyzed extensively, lyophilized, and tested in subcultures of keratinocytes in MCDB 153 medium with 0.1 mM Ca++ containing only defined supplements (insulin, hydrocortisone, transferrin, ethanolamine, phosphoethanolamine). Cells plated in the absence of EGF at moderately high densities (1000-3000 cells per cm2) formed colonies and grew in the presence of placental extract at 25-500 micrograms/ml. Extracts of cord serum or maternal serum were inactive, suggesting that the activity is derived from placental tissue. The activity is not EGF, since the activity in the placental extract, unlike EGF, did not promote growth at low cell density, was synergistic with EGF under some conditions, and did not produce changes in colonial morphology which occurred in the presence of EGF. Unlike keratinocyte growth-promoting activity in bovine hypothalamic extract, the activity is non-dialyzable and is destroyed at 100 degrees C. Placental extract could not replace any of the defined components of the medium and is therefore distinct from them. The presence of activity in the placenta with distinctive properties suggests that this is a previously undescribed material with growth-promoting properties for epithelium.     

Steroid 21-sulfatase activity in human placenta

Intravenously administered [3H]-deoxycorticosterone sulfate is not metabolized by way of deoxycorticosterone in men or non-pregnant women. Thus, it can be implied that steroid 21-sulfatase is not active in human tissues. On the other hand, evidence has accrued that deoxycorticosterone sulfate is hydrolyzed in human placenta. In the present investigation, we sought to ascertain if steroid 21-sulfatase activity were present in placenta and, if so, to characterize the enzyme activity in this tissue. Steroid 21-sulfatase activity was found to be present in microsome-enriched fractions prepared from human placental tissue; conditions of linearity of the reaction with time and protein concentration were established and the apparent KM of the enzyme for deoxycorticosterone sulfate was 100 microM. Thus, deoxycorticosterone sulfate, which is present in high concentration in plasma of the human fetus, may enter trophoblast wherein it could be hydrolyzed; the deoxycorticosterone formed could be secreted into the maternal circulation. Such a process, together with deoxycorticosterone formation from plasma progesterone in extraadrenal sites, could account for the high concentrations of deoxycorticosterone that are present in plasma of near-term pregnant women.     

The activity of glutaminase in the human placenta

Homogenates and extracts of human placenta are able to desamidate glutamine by means of an enzyme which has the properties of glutaminase. Placental glutaminase is activated by phosphate. Its pH optimum lies at 9.0.A method for its assay in placental homogenate is described. It was found that the glutaminase activity decreases toward the end of pregnancy. At this time, the activity, expressed as Q_NH3 (N), amounts to 23.7 ± 6.7.Some quantitative aspects of glutaminase activity in the human placenta and kidney are discussed.     

Partial purification and characterization of a peroxidase activity from human placenta.

The aim of this work was to use preparations from germinating seeds of Pisum sativum to determine the apparent equilibrium constant of the reaction catalysed by sucrose-phosphate synthase (EC 2.4.1.14) and to compare this with the mass-action ratio of the reaction in the seeds. The apparent equilibrium constant ranged from 5.3 at 0.25 mM-MgCl2, pH 7.0, to 62 at 10 mM-MgCl2, pH 7.5. The sucrose phosphate content of the seeds, 23 nmol/g fresh wt., was determined by separating sucrose phosphate from sucrose by ion-exchange chromatography and then measuring the sucrose released by alkaline phosphatase. Comparison of equilibrium constants and mass-action ratios in the cotyledons of 38 h-germinated seeds showed that the reactions catalysed by glucose-6-phosphate isomerase, phosphoglucomutase and UDP-glucose pyrophosphorylase are close to equilibrium, and those catalysed by sucrose-phosphate synthase and sucrose phosphatase are considerably displaced from equilibrium in vivo.     

Lactate dehydrogenase activity in human placenta following exposure to environmental pollutants.

The impact of environmental pollution at the place of residence of pregnant women and of their smoking habits on the cellular energy metabolism of placental tissue was investigated. Samples of full-term placentas were randomly collected from two environmentally different regions of Slovakia (Bratislava, Stará Lubovna) and the activity of lactate dehydrogenase (LDH) was measured. Our results showed enhanced LDH activity in the placenta that was dependent on both the type of environmental pollutants at the place of residence and the smoking habits during pregnancy. The enhanced LDH activity may reflect hypoxic conditions due to the accumulation of heavy metals and toxic compounds of tobacco smoke in the placental tissue. A high content of heavy metal particles, found in placental samples from Stará Lubovna in our previous studies, might contribute to the increased LDH activity in placentas from this region. We hypothesize that fine metal particles deposited in the placental tissue might be phagocytozed by the syncytiotrophoblast, thus contributing to the decreased oxygen level in placental tissue.     

Immunoactive products of human placenta. I. An immunoregulatory factor obtained from explant cultures of human placenta inhibits CTL generation and cytotoxic effector activity

Supernatants were prepared from short-duration explant cultures of term human placentas obtained after cesarean delivery. These supernatants inhibited murine and human mixed lymphocyte reactions, as well as CTL generation. The effects were reversed by an excess of IL-2-containing medium. Similarly, the material inhibited human natural killer cytotoxicity against K 562 targets. The material was subjected to gel-filtration chromatography on an ACA 44 or Bio-Gel A15m column. The apparent MW of the MLR-CML material was about 60-70 kDa, whereas the NK inhibiting activity was eluted in high-MW components (greater than 200 kDa) as well as in the 50-kDa range. The relevance of this material in local immunoregulation during human pregnancy is discussed.     

Oestrone sulphate sulphohydrolase activity in nuclear envelopes from human placenta cell nuclei.

Procedures for isolation, from human term placenta, of highly purified nuclei and nuclear envelopes with a low content of DNA are described. Both fractions contain oestrone sulphate sulphohydrolase activity. The enzyme from nuclear envelopes can be solubilized with Triton X-100 and, partially, with proteolytic enzymes. It does not require Ca2+ and is insensitive to Ag+ and agents reacting with SH groups. It is strongly inhibited by millimolar concentrations of sulphites and to a much smaller extent by phosphates. Oxidized forms of ascorbic acid, glutathione and NAD+ revealed a pronounced inhibitory effect, whereas reduced forms of these compounds produced a slight activation. It is proposed that oestrone sulphate sulphohydrolase activity in nuclear envelopes from human placenta is not exerted by arylsulphatase but represents a specific enzyme.     

Estrogen hydroxylase activity in the human placenta at term

Placental estrogen hydroxylase (EH) enzyme activity was measured at term using the catechol-O-methyl transferase coupled method in normal and high risk conditions. The identity and ratio of products formed during incubation of microsomes as analysed by high performance liquid chromatography in chronic hypertension, toxemia and diabetes mellitus was not different from controls. The mean enzymatic activity was also not different among the conditions studied as expressed mean +/- SE pmol/min/mg, protein: chronic hypertension (7.8 +/- 1), toxemia (8 +/- 1.6), diabetes mellitus (6.1 +/- 0.9) and controls (8.3 +/- 1.5). The cofactor dependence of EH was studied showing that NADPH is a better substrate for the enzyme than NADH.     

Catechol O-methyltransferase activity in the human placenta and liver

Catechol O-methyltransferase (COMT) obtained from human liver (HL) and human placenta (HP) was found to be much less active than rat liver (RL) COMT when norepinephrine, epinephrine, dopamine, and isoproterenol are used as substrates. The Km values, which reflect the affinity of substrate and enzyme, show that RL COMT has the highest affinity toward the catecholamine substrates followed by HP COMT and then HL COMT. Both HP and RL COMT preparations O-methylate the catecholamines primarily in the meta position.