[en] Cysteinesulfinate decarboxylase (CD), a pyridoxal 5'-phosphate-dependent enzyme, is believed to be rate-limiting for taurine biosynthesis in the rat. Although taurine is synthesized by the pup, it is abundant in milk of the lactating rat. CD activity has been shown to be reduced in vitamin B6-deficient, lactating rats and their pups, without much change in taurine concentration of certain tissues. To further understand the effect of B6 status of lactating rats on taurine biosynthesis and availability to their pups, pregnant dams were fed either a B6-deficient or B6-adequate (20 mg/kg) diet during gestation and 10 days postpartum. After this time period, all dams were gavaged ³⁵S cysteine and ³H taurine, milk and tissues of the dams and pups collected, and taurine isolated by ion-exchange chromatography. There was no difference in the ³⁵S/³H ratio in the heart or liver for the adequate and deficient dams. The ³⁵S/³H ratio was slightly but significantly greater in the liver of the B6-adequate pups compared to the B6-deficient pups without a difference in the level of ³H taurine (pmol/gram protein) in the milk or pup's liver. Results indicate that a B6 deficiency can influence taurine biosynthesis in the pup without impairing secretion of taurine in milk

[en] The influence of serum, IGF-1 and TGF-β on the differentiation of preadipocytes was examined in primary cultures of porcine adipose tissue cells. In serum-supplemented or serum-free, IGF-1 (1 and 10 nM) had no effect on total cell number. However, IGF-1 (10nM) increased adipocyte number only in serum-supplemented (1% pig serum) cultures, whereas TGF-β (15 pm) reduced the adipocyte number in the presence and absence of IGF-1. Replication of preadipocytes was analyzed with a [³H] thymidine assay. Preadipocyte proliferation (cpm in adipocyte fraction) was increased by IGF-1 (10nM) only in cultures containing pig serum. TGF-β had no effect on preadipocyte proliferation specifically, but slightly increased total [³H] thymidine incorporation in cultures with serum. Glycerol phosphate dehydrogenase (GPDH) specific activity was decreased by adding TGF-β to serum-free cultures but TGF-β had little effect in serum-supplemented cultures. Cellular secretion of IGF-1 was decreased when TGF-β was added to serum-free or serum-supplemented cultures. These studies indicate that TGF-β does not inhibit adipocyte development in the initial growth phase, but may inhibit differentiation and/or hypertrophy at a later stage of development

[en] [11,12-³H] all-trans Retinol and various detergents were added to homogenates of fresh bovine retinal pigment epithelium. After dark incubation for 40 minutes at 37 degrees C, the retinoids were extracted and analyzed by a high resolution HPLC method. The detergents showed different effects on the retinyl ester synthetase (RES) and all-trans:11 cis retinoid isomerase (RI) activities. The detergent CHAPS (0.3%) almost totally destroyed RI activity without reducing RES activity. The same concentration of sodium dodecyl sulfate and Nonidet P-40 significantly reduced RES activity and totally destroyed RI activity. RES and RI activities were unaffected by 0.3% Mega 8, a nonionic detergent, but were inhibited by 1% Mega 8. Thus, because of these differential effects of detergents, RES and RI probably are different enzymes rather than a single multifunctional enzyme. Because isomerization was always inhibited more than esterification, our findings also accord with the esterification/isomerization mechanism recently reported by Rando et al

[en] The intestinal absorption and in vivo turnover kinetics of [³H]folic acid (FA) and (6S)-5-formyl-[³H]tetrahydrofolate (5-CHO-THF) were examined to determine whether differences exist in the inherent bioavailability of these forms of the vitamin. Following oral administration of 2 μCi/100 g body weight (in 50 mM sodium ascorbate, pH 7), a biphasic pattern of urinary tritium excretion was observed for each labeled folate. The following kinetic results were obtained (n=9). Little tritium was found in the GI tract after 8 hours, which indicated nearly complete absorption of each folate. HPLC analysis of urine revealed similar excretory patterns over 0-8 days post-dose for each folate administered, and the patterns of hepatic [³H]folates were equivalent when examined after 8 hours and 4 days post-dose. These findings indicate that the bioavailability FA and 5-formyl-THF is equivalent

[en] Human β-casein is a major protein in human milk. This protein is part of the casein micelle and has been suggested to have several physiological functions in the newborn. Since there is limited information on βcasein and the factors that affect its concentration in human milk, the authors have isolated and sequenced the gene for this protein. A human mammary gland cDNA library (Clontech) in gt 11 was screened by plaque hy-hybridization using a 42-mer synthetic ³²p-labelled oligo-nucleotide. Positive clones were identified and isolated, DNA was prepared and the gene isolated by cleavage with EcoR1. Following subcloning (PUC18), restriction mapping and Southern blotting, DNA for sequencing was prepared. The gene was sequenced by the dideoxy method. Human β-casein has 212 amino acids and the amino acid sequence deducted from the nucleotide sequence is to 91% identical to the published sequence for human β-casein show a high degree of conservation at the leader peptide and the highly phosphorylated sequences, but also deletions and divergence at several positions. These results provide insight into the structure of the human β-casein gene and will facilitate studies on factors affecting its expression

[en] The development of appropriate placental trophoblast isolation and culture techniques enables the study of pathways of glucose utilization by this important cell layer in vitro. Trophoblasts from normal term placentas were isolated and cultured 24 hours and 72 hours in uncoated polystyrene culture tubes or tubes previously coated with a fibrin matrix. Trophoblasts cultured on fibrin are morphologically distinct from those cultured on plastic or other matrices and generally resemble in vivo syncytium. Cells were incubated up to 3 hours with ¹⁴C-labeled glucose and reactions were stopped by addition of perchloric acid. ¹⁴CO₂ production by trophoblasts increased linearly with time however the largest accumulation of label was in organic acids. Trophoblasts cultured in absence of fibrin utilized more glucose and accumulated more ¹⁴C in metabolic products compared to cells cultured on fibrin. Glucose oxidation to CO₂ by the phosphogluconate (PG) pathway was estimated from specific yields of ¹⁴CO₂ from [1-¹⁴C]-D-glucose and [6-¹⁴C]-D-glucose. Approximately 6% of glucose oxidation was by the PG pathway when cells were cultured on fibrin compared to approximately 1% by cells cultured in the absence of fibrin. The presence of a fibrin growth matrix appears to modulate the metabolism of glucose by trophoblast from human placenta in vitro

[en] Small differences in dietary fats cause marked differences in cholesterol metabolism in different strains of mice. CBA/J mice adjust HMGCOA reductase activity and C57BR/cdJ mice change fecal excretion of cholesterol. Phenomenological compartmental modeling of movement of 4¹⁴C-cholesterol in the two strains of mice fed 40 en % fat, P/S = 0.24 (SFA) or 30 en % fat, P/S = 1 (PUFA) was used to analyze rates of movement between serum, liver, heart, and carcass. The C57 mice had slower movement between all compartments than CBA. Residence times in tissues were longer in mice fed SFA than those fed PUFA diet. The kinetic results are in agreement with the organ concentrations and enzyme activities measured

[en] Little is known about regional myocardial blood flow and metabolism in the developing heart. Simultaneous estimates of regional myocardial blood flow and glucose metabolism have been made in the adult rat by Yonekura et al using [²⁰¹] Thallium (THAL) and [¹⁴C]2-deoxyglucose (DG) autoradiography. Since glucose is the primary cardiac metabolic substrate during development, glucose utilization is also an estimate of myocardial metabolism. Examination and comparison of the THAL and DG autoradiographs revealed that there is an uncoupling of blood flow and metabolism in the developing chick heart. Areas of the heart which had marked glucose utilization did not always have marked blood flow. Regions of the heart which had marked blood flow but very little glucose utilization were the interventricular septum and the apex. One explanation for this disparity is that although blood flow may be established in these regions, normal cardiac function requiring significant substrate utilization may not be fully developed

[en] Basolateral membrane vesicles (BLMV) were isolated from Atlantic lobster (Homarus americanus) hepatopancreas and purified by discontinuous sucrose gradient centrifugation. BLMV prepared in this fashion were osmotically reactive exhibiting linear dependence of vesicular ³⁵SO₄^-2 uptake to increasing external osmotic pressure with negligible non-specific isotope binding. Under short circuited conditions (valinomycin/K⁺) BLMV responded to either a HCO₃^- gradient directed out or equilibrated HCO₃^- (10 mM) by displaying short term accumulation of sulfate above that of equilibrium. Uptake of divalent anion was unaffected by an inwardly directed transmembrane Na⁺ or tetramethylammonium⁺ gradient. ³⁵SO₄^-2/HCO₃^- exchange in the presence of valinomycin was stimulated by transient inside positive K⁺ diffusion potentials and inhibited by transient inside negative K⁺ diffusion potentials. The role of electrogenic anion exchange by hepatopancreas BLMV in transcellular sulfate transport is discussed

[en] In the present studies, the binding of [¹²⁵I]aFGF was characterized in a membrane preparation from NIH 3T3 cells transfected with the human flg gene. The inclusion of heparin was necessary to reduce nonspecific binding which accounted for approximately 20-30% of total binding. However, heparin in concentrations ranging from 0.1-100 U/ml was not found to significantly alter specific binding. Specific binding was maximal in the presence of 200 mM NaCl. Under these conditions, saturation studies indicated that [¹²⁵I] aFGF bound with high affinity to a single class of recognition sites. aFGF potently inhibited the binding of 0.1 nM [¹²⁵I]aFGF. Several glycine-substituted point mutations of aFGF were also found to inhibit binding with the following order of activity: 137G > 134G = 143G. The present results indicate that the specific binding of [¹²⁵I]aFGF to the aFGF receptor in NIH 3T3 cell membranes provides a reliable assay for the further analysis of the contributions of the aFGF receptor to mammalian physiology