Search PubMed⌕ Search

Biomedical subjects

R N Etingof

Publications and source records attributed to R N Etingof.

At least 19 recordsLinked to original sources
PubMed2000

The effects of melatonin and L-DOPA on the diurnal rhythms of free amino acids content in the rat retina.

The effects of melatonin and dopamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) intraperitoneal administration on the rhythms of free amino acids content in the retina of rats were studied. The authors found that the levels of those amino acids, which are protein constituents but not neurotransmitters in the rat retina, change diurnally with maximum at 3-6 h after light onset. Diurnal changes of Ala, Arg, Asn, Ile, Met, Ser, Trp, and Val content persisted in the retina of rats maintained at constant darkness. This fact confirms the true circadian nature of these rhythms. Constant lighting abolished diurnal changes of the content of all amino acids with the exception of Trp. Daytime but not nighttime administration of melatonin decreased the levels of Ala, Asn, Gln, Ile, Met, and Ser down to nocturnal values. Diurnal changes of amino acids content vanished in melatonin-injected rats. The effect of melatonin administration disappeared when the protein synthesis was inhibited by cycloheximide. The effect of intraperitoneal administration of L-DOPA on the levels of free amino acids was opposite the effect of melatonin administration. L-DOPA increased nocturnal levels of Gly, Thr, Trp, and Val but had no effect on the daytime amino acids content. As in the case of melatonin administration, significant diurnal changes of amino acid levels disappeared in L-DOPA-injected rats. The authors hypothesize that melatonin and dopamine can serve as zeitgebers-antagonists of amino acids content rhythms in the rat retina.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1999

Purine biosynthesis de novo in bovine retina: purification and characterization of amidophosphoribosyl transferase and phosphoribosyl pyrophosphate synthetase.

The ability of bovine retina to synthesize purines de novo is shown for the first time. Amidophosphoribosyl transferase (EC 2.4.2.14), the enzyme controlling the rate of the process, and phosphoribosyl pyrophosphate synthetase (EC 2.7.6.1), the enzyme regulating the intracellular contents of phosphoribosyl pyrophosphate (PRPP), were purified and characterized. The molecular masses of the enzyme subunits are similar to those of the purified enzyme from the liver. The molecular masses of amidophosphoribosyl transferase, PRPP synthetase catalytic subunit, and two PRPP synthetase-associated proteins are 50, 34, 39, and 41 kD, respectively. The apparent Km values of the enzymes and coenzymes are similar to those of the purified enzymes from the liver. For amidophosphoribosyl transferase, the apparent Km for Gln and PRPP are 0.75 +/- 0.05 and 0.66 +/- 0.09 mM, respectively (the corresponding Vmax values are 59 +/- 3 and 136 +/- 12 nmoles PPi/min per mg protein). For PRPP synthetase, the apparent Km for ribose-5-phosphate and ATP are 37.9 +/- 0.5 and 53 +/- 7 microM, respectively (the corresponding Vmax values are 61 +/- 4 and 52 +/- 3 nmoles PRPP/min per mg protein). The sensitivity of the retinal PRPP synthetase to inhibition by ADP and AMP was significantly lower than that of the enzyme from the liver.

Amidophosphoribosyltransferase↗
PubMed1997

Membranes of retinal microsomes: a new protein of the microsomal monooxigenase system.

A new component, which substitutes cytochrome P-450 as an acceptor of reducing equivalents from NADPH-cytochrome P-450 reductase, was identified in the bovine retina microsomal monooxigenase system, which does not contain cytochrome P-450. This component is a non-heme iron-containing protein with molecular mass of 66 kDa. The properties of the protein from the bovine retina are similar to those of MIP, a non-heme iron-containing protein from the heart microsomal monooxigenase system, in which cytochrome P-450 was not identified, either. Activation of the microsomal monooxigenase system (an increase in the NADPH-cytochrome P-450 reductase activity, an increased rate of microsomal NADPH oxidation) was shown in the retina upon long-term intensive illumination. It was shown also that the development of hereditary degeneration of the retina in rats was accompanied by activation of the specific microsomal monooxigenase system in the target tissues (retina, brain cortex) irrespective of its composition (cytochrome P-450 or non-heme iron-containing protein).

Animals↗
PubMed1988

Active sites of the cyclic GMP phosphodiesterase gamma-subunit of retinal rod outer segments.

Monoclonal antibodies were prepared to the gamma-subunit of the cGMP phosphodiesterase. One of them gamma p-1, suppresses the activation of phosphodiesterase through the alpha-subunit of transducin. The gamma-subunit fragment 24-45 rich in Arg and Lys residues is involved in gamma p-1 binding and is essential for the gamma-subunit interaction with transducin. Carboxypeptidase Y cleaves off seven amino acid residues from the C-terminus of the gamma-subunit resulting in phosphodiesterase activation. Thus, the C-terminal fragment of gamma-subunit participates in phosphodiesterase inhibition.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1988

[The role of GTP-binding proteins in the olfactory reception of vertebrates].

The inhibitory effect of the non-hydrolyzable GTP analog Gpp (NH) p (10(-5)-10(-3) M) on the specific binding of some natural odorants (L-3H-amino acids, boar sex pheromone analog 5 alpha-3H-androstan-3-one) and sex hormones (17 beta-3H-estradiol, 3H-testosterone and 5 alpha-3H-dihydrotestosterone) to the olfactory receptors of some vertebrates (fish, frog, sow, rat) was found. Under the same experimental conditions Gpp (NH) p did not affect the high affinity binding of 5 alpha-3H-androstan-3-one to the sow respiratory tissue preparations. It was assumed that the changes in the specific binding of odorants in the presence of guanyl nucleotides can be a suitable test for the identification of true odorant receptors which conjugate with the system of olfactory transduction through G-proteins. The existence of two forms of high affinity GTPase in the olfactory tissue was demonstrated. One of them is an integral membrane component, whereas the second one is a loosely bound to the membrane and it can be solubilized in the presence of EDTA. The role of G-proteins in the system of olfactory transduction and the problem of odorant receptor identification are discussed.

Animals↗
PubMed1988

[The peptide activator of cyclic nucleotide phosphodiesterases: its effect on muscle contractile activity].

The presence of the peptide activator of cyclic nucleotide phosphodiesterase, which has been discovered previously in rat and calf myometrium, was studied in different rat tissues. The peptide was shown to present only in muscle tissues, except for intestinal tissue. In physiological experiments the peptide stimulated the contraction of rat uterine smooth muscle and diaphragmatic muscle. Phosphodiesterase inhibitors reduced this effect of the peptide. It is suggested that the effects of peptide are related to the changes in cyclic nucleotide levels in consequence of phosphodiesterase activation. Peptide did not change the activity of uterine adenylate cyclase.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1987

[Detection of peptide, an activator of cyclic nucleotide phosphodiesterases, in uterine tissue].

The soluble fraction of uterine tissue was found to contain a factor which is a potent activator of various cyclic nucleotide phosphodiesterases (with the exception of the retinal photoreceptor cell enzyme). The protein origin of this factor was established, using proteolysis, precipitation with trichloroacetic acid. The activator was purified by gel filtration on Sephadex G-25 and Biogel P-4 as well as by a highly effective liquid chromatography. The activator was shown to be a peptide with Mr = 1150 Da. The peptide was thermostable and stable within a broad range of pH. Besides phosphodiesterases, the peptide activated 5'-nucleotidase and Mg2+-ATPase of photoreceptor membranes.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1987

[Methylation of 3',5'-cGMP phosphodiesterase in retinal photoreceptor membranes].

It was found that the level of methylation of phosphodiesterase (EC 3.1.4.17) and of proteins with Mr 61000 and 21000-26000 Da in isolated preparations of bovine retinal outer segments was sharply increased in the presence of cGMP, but not with cAMP. Preparations of the outer segment phosphodiesterase protein inhibitor, which inhibits the cyclic nucleotide hydrolysis, significantly decreased the methylation level. The degree of the enzyme methylation depended on the functional state of the outer segments: in light-induced preparations it was higher that in the dark ones.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1987

[Receptors of the olfactory cells: the problem of their identification and characteristics].

Own and some last literary data on the vertebrate olfactory receptors are summarized. Special attention is devoted to the identification of these receptors. The connection of these receptors with the proteins binding the guanosine triphosphate is demonstrated. On this basis a biochemical test to elicit the olfactory receptors is proposed. Using the boar pheromon receptor the application of this test to differentiate the true olfactory receptor and a respiratory lining component that binds the pheromon with the same characteristics like the receptor is shown. The olfactory receptors may be represented no only by the integral but also by peripheric membrane proteins. The questions on the olfactory mucosa receptors and mechanism of the signal transduction in the olfactory cell have been discussed.

Animals↗
PubMed1986

Immunochemical study of the cyclic nucleotide system of retinal photoreceptor membranes: antibodies raised to phosphodiesterase, its protein inhibitor and GTP-binding proteins.

Monospecific precipitating antibodies raised to phosphodiesterase, its protein inhibitor and GTP-binding proteins of bovine retina photoreceptor membranes were obtained. The characterization of the antibodies was carried out by immunochemical methods and according to their functional properties as determined by their effect on enzyme activities. The antibodies were used to study the distribution of immunolike proteins in different animal retinas and to purify the inhibitor protein by the method of immunoaffinity chromatography.

Animals↗
PubMed1984

Estradiol receptor and cyclic nucleotide phosphodiesterase: functional relationship, possible role of guanine nucleotide binding proteins.

The inhibitory effect of estradiol (10(-9)M - 2 X 10(-5)M) on the cyclic nucleotide phosphodiesterase (EC 3.1.4.17) activity of cytosol from rat uterine tissue and human myometrium and endometrium was established. The hormone action was shown to disappear due to preparative separation of the receptor and the enzyme; the effect reappeared after protein mixing. In the presence of GTP, Gpp (NH)p, NaF and cholera toxin the estradiol action on the phosphodiesterase activity was significantly decreased or failed to be revealed. The antibodies raised against G-proteins of retina photoreceptor membranes abolished the hormone action on phosphodiesterase. A conclusion is drawn that in uterine tissue there exists a functional connection between estradiol receptor and phosphodiesterase. The necessary participation of G-proteins in signal transmission is postulated.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

[Comparative immunochemical characteristics of different phosphodiesterases of cyclic nucleotides].

Precipitating monospecific antibodies against purified bovine retinal rod outer segment phosphodiesterase (EC 3.1.4.17) were obtained from rabbit blood serum. These antibodies do not form precipitating complexes with phosphodiesterase isolated from rat or ox brain tissues or from the heart, lung, liver, kidney, testes and uterus of the rat. The antibodies inhibit the activity of retinal rod outer segment phosphodiesterase or that of rat brain, liver, heart and uterus enzyme (despite the lack of precipitation) but have no effect on the phosphodiesterase activity of preparations obtained from rat lungs, kidney or testes. The same effect on the phosphodiesterase activity of all these tissues is exerted by monovalent fragments of the antibodies. Using partially purified preparations of phosphodiesterase from retinal rod outer segments and brain of the ox and from human myometrium, the mechanisms of inhibition of the enzyme catalytic activity by the antibodies was studied. In the presence of the antibodies, the Km and V values appeared to be different, depending on the preparation. It was assumed that a certain site in the phosphodiesterase molecule is characterized by great structural rigidity. Taking into account the shifts in the Km values induced by the antibodies, the differences in the localization of the antigenic determinant in relation to the enzyme active center are discussed.

Animals↗
PubMed1984

[GTP-binding proteins of the retinal photoreceptor membranes: purification, antibodies].

A scheme of immunization of rabbits with partially purified GTP-binding proteins isolated from ox retinal photoreceptor membranes has been developed. Using double radial immunodiffusion, it was shown that rabbit antiserum interacts with the GTP-binding proteins of the retinal phosphoreceptor membranes of ox, pig and frog. The antibodies interaction with the GTP-binding proteins of ox retinal rod outer segments was followed by immunoelectrophoresis as well as by elimination of the activating effect of the non-hydrolyzable derivative of GTP, guanyl-5'-yl-imidodiphosphate on cyclic nucleotide phosphodiesterase in illuminated photoreceptor membranes and in their extracts. A similar effect was exerted by immunoglobulins from immunized animals on the enzyme activation by NaF. Purified immunoglobulins type G did not practically interact with the GTP-binding proteins of the photoreceptor membranes.

Animals↗
PubMed1984

[The presence of calmodulin in chemosensory structures, its purification and content].

Chemosensory tissues, bovine olfactory epithelium and barbel of dwarf sheat-fish (Ictalurus nebulosus) rich in gustatory buds were shown to contain calmodulin. The fraction of thermostable proteins which activate brain phosphodiesterase of cyclic nucleotides was purified to homogeneity by stepwise ion-exchange chromatography on DEAE-cellulose and gel filtration on Sephacryl S-300. Some properties of calmodulin from chemosensory tissues (e. g., content, molecular weight, electrophoretic mobility, degree of activation of phosphodiesterase) are similar to those of brain calmodulin.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗