Biomedical subjects
Publications and source records attributed to M Altstein.
Benzodiazepine receptors are present in high concentration in the chick retina. Their pharmacological properties are similar to those of the benzodiazepine receptors present in the brain. The retina receptors appear prior to, as well as during, the period of synaptogenesis. In the newborn chick retina the receptors are localized in the inner synaptic layer, probably on or close to synaptic connections.
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Two distinct enzymatic activities capable of hydrolyzing enkephalin are present in the brain. The major activity was shown to be a neutral aminopeptidase which hydrolyzes Leu-enkephalin (Leu-Enk) with a Km of 2 X 10(-5) M. This activity was inhibited by heavy metal ions (i.e. Zn++, Cd++), by sulfhydryl blocking reagents, and by the antibiotics bacitracin and puromycin. In contrast, these two antibiotics had no effect on the hydrolysis of Leu-Enk by either rat serum or commercial leucine aminopeptidase. The integrity of both the glycosidic and peptide bonds in the puromycin molecule was required for its inhibitory activity. On the other hand, modifications of the sugar moiety had relatively little effect, allowing the design of puromycin analogs which were inactive with regard to protein synthesis inhibition but still capable of inhibiting brain aminopeptidase. Puromycin was also shown to inhibit enkephalin degradation by homogenates of guinea pig ileum and to prolong the depressant effect of enkephalin on the electrically induced contractions of the ileum. The second enzymatic activity in brain homogenate was found to sediment with the synaptic plasma membrane fraction and cleave Leu-enkephalin into Tyr-Gly-Gly and Phe-Leu with a Km of 2.2 X 10(-5) M and pH optimum between 6.5 and 7.0. This endopeptidase was inhibited by metal chelating agents and by thiols but was insensitive to puromycin and to p-chloromercuribenzoate. In contrast to the aminopeptidase some cleavage of (D-Ala2)Met-Enk x amide by the endopeptidase was observed.
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The binding of [(3)H]tyrosyl-PBAN28-33NH(2) to pheromone gland membranes of the moth Heliothis peltigera was investigated. The study describes the development of a pheromone biosynthesis-activating neuropeptide (PBAN) radioreceptor assay and demonstrates the presence of a putative PBAN binding site on the pheromone gland. It also describes synthesis of a radioligand and optimization of binding conditions with respect to membrane preparation, number of gland equivalents, kinetics of ligand binding and composition of the binding solution. Binding was found to be optimal when membranes were freshly prepared from frozen glands, incubated at a concentration of one gland equivalent per reaction tube in the presence of 10 mM HCO(3)(-) ions. Equilibrium of ligand binding was obtained after 20 min. Presence of other components such as NaCl, KCl or SH reagents did not have any effect on binding. Binding was found to be saturable, with a K(d) of 5.73 +/- 1.05 x 10(-6) M and a Bmax of 1.85 +/- 0.22 nmol/mg protein. Binding was effectively displaced by unlabeled PBAN1-33NH(2) and PBAN28-33NuEta(2) with a K(i) of 4.3 +/- 1.1 x 10(-6) M and 4.9 +/- 2.6 x 10(-6) M, respectively.