The structure of N-acetylaspartylglutamate (NAAG) suggests this neuronal dipeptide as a candidate for interaction with discrete subclasses of ionotropic and metabotropic acidic amino acid receptors . A substantial difficulty in the assay of these interactions is posed by membrane-bound peptidase activity that converts the dipeptide to glutamate and N-acetylaspartate, molecules that will interfere with receptor assays . We have developed two sets of unique receptor assay conditions and applied one standard assay to measure the interactions, under equilibrium binding conditions, of [ 3 H]kainate, [ 3 H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([ 3 H]AMPA), and [ 3H]CGS-19755 with the three classes (kainate, quisqualate, and N-methyl-D-aspartate) of ionotropic glutamate receptors, while inhibiting peptidase activity against NAAG . Under these conditions, NAAG exhibits apparent inhibition constants (IC5o) of 500, 790, and 8 .8 pM in the kainate, AMPA, and CGS-19755 receptor binding assays, respectively. Glutamate was substantially more effective and less specific in these competition assays, with inhibition constants of 0 .36, 1 .1, and 0 .37 ftM. These data support the hypothesis that, relative to glutamate, NAAG functions as a specific, low potency agonist at N-methyl-D-aspartate subclass of ionotropic acidic amino acid receptors, but the peptide is not likely to activate directly the kainate or quisqualate subclasses of excitatory ionotropic receptors under physiologic conditions . Key Words: lonotropic glutamate receptors-Kainate-Quisqualate-NMDA receptors-CGS-19755-Amino-3-hydroxy-5-methylisoxazole-4propionic acid-N-Acetylaspartylglutamate-Neuropeptide .

The effect of thyroidectomy (Tx) on some key enzymes involved in glycolysis and the HMP-shunt pathway were studied in the testis of pre-pubertal, pubertal and adult rats. Hexokinase (HK) and phosphofructokinase (PFK) did not show any significant change in activity after Tx. However, pyruvate kinase (PK) activity was reduced after Tx in the testis of pre-pubertal animals although in pubertal and adult rats it was not affected. Both glucose-6-phosphate dehydrogenase (G6P-DH) and 6-phosphogluconate dehydrogenase (6-PG-DH) activities were reduced after Tx and thyroxine (T4) replacement brought both enzyme activities back towards normal. The possible effect of the thyroid on testicular steroidogenesis acting through the HMP-shunt is discussed.

Micro lipid droplets fuse with each other in vivo to form larger precursors of milk lipid globules. The extent of fusion dictates the size range of lipid globules in milk. A cell-free system in which micro lipid droplet fusion can be induced has been developed. Fusion was promoted by calcium and a protein complex from cytosol. Exogenously supplied gangliosides were potent fusion-promoting agents. Endogenous gangliosides were detected on micro lipid droplet surfaces by immunocytochemical localization. Monoclonal antibody to disialyllactosylceramide (GD3) inhibited micro lipid droplet fusion. These observations are suggestive of a role for gangliosides in micro lipid droplet fusion in situ.

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