Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.36 (hyaluronidase)
 4,606 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A procedure has been developed for the isolation of cone photoreceptors from the retina of the lizard Anolis carolinensis in order to study the effects of dark- and light-adaptation on the cyclic nucleotide metabolism of these visual cells. Incubation of the retina in N2 medium with hyaluronidase and DNAase allows us to obtain intact photoreceptors with good purity (85-90%), yields (greater than 2 x 10(5) cells per retina), and more than 95% of them excluding Trypan blue. cAMP levels are 20-fold higher than cGMP levels in cells from dark-adapted animals and are decreased by 35% upon exposure to light, whereas cGMP levels show no apparent change. However, both cAMP- and cGMP-phosphodiesterases, as well as adenylate and guanylate cyclase, are activated several-fold by light, but the enzymes involved in cGMP metabolism have higher Vmaxs than the cAMP related enzymes. The apparent constant levels of cGMP found in cone photoreceptors may result from our inability to detect the very fast changes that occur in these cells when they are exposed to light.
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PMID:The effects of light on cyclic nucleotide metabolism of isolated cone photoreceptors. 134 77

The properties of gonadotropin-releasing hormone (GnRH) receptors were analyzed in isolated pituitary cells prepared by enzymatic dispersion with trypsin or collagenase-hyaluronidase. The initial impairment of LH responses to GnRH in isolated cells prepared by both methods was reversed during culture for 2 days in multiwell vessels. However, specific binding sites for GnRH, assayed by equilibration with [125I]iodi0[D-Ser(t-BU)6]des-Gly10-GnRH N-ethylamide (GnRH-A) were demonstrable in collagenase-dispersed cells, both initially and after 2 days in culture. Cellular uptake of GnRH-A was temperature dependent, with rapid and saturable binding to a limited number of specific receptor sites with high affinity for the labeled analog (Ka = 4.0 +/- 0.8 X 10(9) M-1). These sites showed common binding specificity for GnRH-A and the native GnRH peptide, with significantly lower affinity for the natural peptide (Ka = 2.3 X 10(7) M-1). Other protein and peptide hormones, including ovine LH, ovine PRL, hCG, TRH, somatostatin, and angiotensin II (up to 10(-6) M) did not inhibit binding of GnRH-A to its receptors. Cellular binding of GnRH-A was followed by increased cGMP production and LH release within 10 min. The analog was 50 times more potent than native GnRH in stimulating LH release. The Kact values derived for GnRH and GnRH-A were 0.5 and 0.01 nM, respectively, considerably lower than the Kd values of 50 and 0.25 nM derived from receptor binding analysis. These results indicate that GnRH receptors can be identified in isolated pituitary cells, in which peptide binding is followed by increased cGMP production and LH release. The impaired LH responses in acutely dispersed pituitary cells are not due to the loss of receptor sites but to a reversible postreceptor defect. Occupancy of about 20% of the GnRH-binding sites elicits a near-maximal LH response, indicating the nonlinearity of GnRH-receptor coupling to secretory responses in the cultured gonadotroph.
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PMID:Characterization of gonadotropin-releasing hormone receptors in cultured rat pituitary cells. 625 Jul 93