Effect of beta-hydroxybutyrate and acetoacetate on insulin and glucagon secretion from perfused rat pancreas

To elucidate the physiological significance of ketone bodies on insulin and glucagon secretion, the direct effects of beta-hydroxybutyrate (BOHB) and acetoacetate (AcAc) infusion on insulin and glucagon release from perfused rat pancreas were investigated. The BOHB or AcAc was administered at concentrations of 10, 1, or 0.1 mM for 30 min at 4.0 ml/min. High-concentration infusions of BOHB and AcAc (10 mM) produced significant increases in insulin release in the presence of 4.4 mM glucose, but low-concentration infusions of BOHB and AcAc (1 and 0.1 mM) caused no significant changes in insulin secretion from perfused rat pancreas. BOHB (10, 1, and 0.1 mM) and AcAc (10 and 1 mM) infusion significantly inhibited glucagon secretion from perfused rat pancreas. These results suggest that physiological concentrations of ketone bodies have no direct effect on insulin release but have a direct inhibitory effect on glucagon secretion from perfused rat pancreas.     

The isolation and characterisation of a cDNA clone for human lecithin:cholesterol acyl transferase and its use to analyse the genes in patients with LCAT deficiency and fish eye disease

We have isolated cDNA clones coding for human lecithin:cholesterol acyl transferase (LCAT) from a liver-specific cDNA library by the use of two oligonucleotide probes based on the protein sequence. The clones span the sequence coding for the entire secreted LCAT, the 3' untranslated sequence and 12 amino acids of the signal peptide. The peptide sequence contains the conserved active site of serine lipases within a hydrophobic domain, flanked by a possible amphipatic alpha-helix. Only one gene for LCAT could be detected in genomic blots. We have used the cDNA as a probe to analyse the LCAT gene in patients suffering from LCAT deficiency and fish eye disease. No rearrangements or abnormal gene fragments were detected in these patients.     

2,3-Bisphosphoglycerate protects mitochondrial and cytosolic proteins from proteolytic inactivation

2,3-bisphosphoglycerate at physiological concentration similar to that found in many tissues protects effectively ornithine transcarbamoylase (OTC) from proteolytic inactivation by broken lysosomes. 2,3-bisphosphoglycerate protects also many other mitochondrial and cytosolic proteins, such as glutamate dehydrogenase (GDH) an glyceraldehyde-3-phosphate dehydrogenase (GAPDH), from proteolysis by broken lysosomes and other proteases. It is, thus, suggested that 2,3-bisphosphoglycerate may play an important role in the control of the degradative rates of some proteins, which may explain its high concentration in certain cells.     

Interactions of the receptor for insulin-like growth factor II with mannose-6-phosphate and antibodies to the mannose-6-phosphate receptor

Recently, the sequence of the human receptor for insulin-like growth factor II (IGF-II) was found to be 80% identical [Morgan et al., (1987) Nature 329, 301-307] to the sequence of a partial clone of the bovine cation-independent mannose-6-phosphate receptor [Lobel et al., (1987) Proc. Natl. Acad. Sci. USA 84, 2233-2237]. In the present study, the purified receptor for insulin-like growth factor II (IGF-II) was found to react with two different polyclonal antibodies to the purified mannose-6-phosphate receptor. Moreover, mannose-6-phosphate was found to stimulate the binding of labeled IGF-II to the IGF-II receptor by two-fold. This effect had the same specificity and affinity as the reported binding of mannose-6-phosphate to its receptor; mannose-1-phosphate and mannose had no effect on the binding of labeled IGF-II to its receptor, and the half-maximally effective concentration of mannose-6-phosphate was 0.3 mM. Also, mannose-6-phosphate did not affect labeled IGF-II binding to the insulin receptor. These results support the hypothesis that a single protein of Mr-250,000 binds both IGF-II and mannose-6-phosphate. Furthermore, they indicate that mannose-6-phosphate can modulate the interaction of IGF-II to its receptor.     

High affinity binding of human interleukin 4 to cell lines

Purified human recombinant interleukin 4 (IL-4) was radio iodinated to high specific radioactivity without loss of biological activity. 125I-IL-4 bound specifically to the Burkitt lymphoma Jijoye cells and other cell lines. Jijoye cells showed a high affinity for 125I-IL-4 (Kd approximately equal to 7 10(-11) M) and displayed 1200-1400 specific receptors per cell at 4 degrees C or 37 degrees C. The equilibrium dissociation constant (Kd) corresponds to the IL-4 concentration which induces 50% maximal expression of the low affinity IgE receptor (Fc epsilon RL/CD23) on Jijoye cells. At 4 degrees C the rate constant of association K1 is 1.7 x 10(6) M-1 s-1 and the rate contant of dissociation k -1 is 1.3 x 10(-4) s-1 (t 1/2 = 91 min.) No human recombinant lymphokines other than IL-4 were able to compete for the binding of 125I-IL-4 to its receptor.     

Apocytochrome-c competes with pre-ornithine carbamoyl transferase for transport into mitochondria

Apocytochrome c, the cytosolic precursor of cytochrome c, competes with the precursor of ornithine carbamoyltransferase (OCT) for entry into isolated rat liver mitochondria.     

Tandem mass spectrometric determination of 11-dehydrothromboxane B2, an index metabolite of thromboxane B2 in plasma and urine

11-Dehydrothromboxane B2 is one of the major enzymatic metabolites of thromboxane B2 (TXB2), a biologically inactive product of thromboxane A2. The short half-life of thromboxane A2 and ex vivo production of thromboxane B2 by platelet activation make these prostanoid metabolites inappropriate as indices of systemic thromboxane biosynthesis, whereas 11-dehydro-TXB2 has been shown to reflect the release of thromboxane A2 in the human blood circulation. Analysis of 11-dehydro-TXB2 in plasma and urine was performed by gas chromatography-mass spectrometry-mass spectrometry using the chemically synthesized tetradeuterated compound as an internal standard. The high selectivity of triple-stage quadrupole mass spectrometry (tandem mass spectrometry) considerably facilitates sample purification as compared to single quadrupole mass spectrometric determination. Plasma concentrations in five healthy male volunteers were in the range 0.8-2.5 pg/ml. Urinary excretion of 11-dehydro-TXB2 was higher than that of 2,3-dinor-TXB2: 1.2 +/- 0.36 micrograms/24 h vs 0.53 +/- 0.33 micrograms/24 h (n = 5). Thus 11-dehydro-TXB2 appears at present to be the best index metabolite of systemic TXA2 activity in plasma as well as in urine.     

Magnetic aqueous two-phase separation: a new technique to increase rate of phase-separation, using dextran-ferrofluid or larger iron oxide particles

A new technique to speed up the phase separation of aqueous two-phase systems is described. The technique is based on the addition of magnetically susceptible additives (ferrofluids or iron oxide particles). In a magnetic field such additives will induce a faster phase separation. In one approach, dextran-stabilized ferrofluid was added to an aqueous two-phase system containing polyethylene glycol and dextran. The ferrofluid was totally partitioned to the dextran phase. After mixing of the two-phase system, it was possible to reduce the separation time by a factor of 35 by applying a magnetic field to the system. Another approach involved the use of 1-micron iron oxide particles instead of ferrofluid. In this case also, the phase-separation time was reduced, by a factor of about 70, when the system was placed in a magnetic field. The addition of ferrofluid and/or iron oxide particles was shown to have no influence on enzyme partitioning or on enzyme activity. The partitioning of chloroplasts, on the other hand, was influenced unless the ferrofluid used had been treated with epoxysilane. A column system comprising 15 magnetic separation stages was constructed and was used for semicontinuous separation of enzyme mixtures.     

Cobinding of bilirubin and sulfonamide and of two bilirubin molecules to human serum albumin: a site model

Differential light absorption spectra of the bilirubin-albumin 1:1 complex, obtained on addition of 20 different sulfonamides, differ with respect to shape and amplitude. This finding seems to indicate that the sulfonamide molecule is bound in direct touch with the bilirubin. The light absorption spectrum of bilirubin-albumin 1:1 undergoes changes on cobinding of a fatty acid anion, laurate, and on variation of pH, previously explained by a change of dihedral angle between the two chromophores of the bilirubin molecule. In bilirubin-albumin 2:1, binding of laurate and variation of pH cause little change of the spectrum. This is best explained by binding of the two bilirubin molecules in close proximity, preventing conformational changes in the complex. From measurements of fluorescence of the lone tryptophan group in albumin and quenching on binding of bilirubin, we calculated the distance of 22 A from tryptophan to the first bound bilirubin molecule, and of 18 A to the second. Mutual quenching of the bilirubin fluorescence from two bound bilirubin molecules seemed to indicate that the two are bound closely together. A model of bilirubin-albumin with a binding site capable of accommodating one bilirubin and one sulfonamide molecule, or two molecules of bilirubin, is compatible with our findings.     

Down-regulation of atrial natriuretic factor receptors and correlation with cGMP stimulation in rat cultured vascular smooth muscle cells

The relationship between the binding of 125I-labeled rat ANF and the responsiveness in cGMP production of ANF receptors were examined in cultured rat thoracic smooth muscle cells after preexposure with the peptide. Binding assay of 125I-labeled ANF showed a specific, reversible and saturable binding with a KD value of 3.1 +/- 0.3 10(-10) M and a maximum binding (Bmax) of 240 +/- 30 fmol/10(6) cells. Pretreatment of the cells with increasing concentrations of unlabeled ANF (10(-9) M to 10(-7) M) resulted in a dose-dependent decrease of the number of binding sites without a change in the affinity. This effect was clearly associated with a desensitization of ANF-induced cGMP production.