RESUMEN
A recombinant bacterial plasmid, pMS1, was constructed that contains 318 nucleotides complementary to a portion of pro-opiolipomelanocortin (proOLMC) messenger RNA from an ectopic adrenocorticotropin-producing tumor. The cloned complementary DNA insert, which contains the sequence that codes for all of the beta-melanocyte-stimulating hormone and beta-endorphin portions of proOLMC, as well as the 3' nontranslated section, is identical to the genomic sequence. Hybridization of tumor proOLMC complementary DNA to RNA subjected to electrophoresis and transferred to a nitrocellulose filter revealed two proOLMC messenger RNA species in the tumor polyadenylated RNA, but only one in pituitary polyadenylated RNA. At least one of the tumor proOLMC messenger RNA's is similar, if not identical, to human pituitary proOLMC messenger RNA.
Asunto(s)
ADN Recombinante/metabolismo , Endorfinas/genética , Hormonas Ectópicas/genética , Hormonas Estimuladoras de los Melanocitos/genética , Hormonas Adenohipofisarias/genética , Precursores de Proteínas/genética , Secuencia de Aminoácidos , Secuencia de Bases , Tumor Carcinoide/fisiopatología , Clonación Molecular , ADN de Neoplasias/genética , Humanos , Masculino , Persona de Mediana Edad , Neoplasias Pancreáticas/fisiopatología , Proopiomelanocortina , ARN Mensajero/genética , betaendorfinaRESUMEN
Goose red blood cells were studied as a model for metabolic regulation of sugar transport. In contrast to their action in human erythrocytes, sulfhydryl-blocking agents such as N-ethylmaleimide (NEM) stimulated 3-O-methylglucose transport markedly in goose red blood cells. The effect of NEM was further enhanced when adenosine 5'-triphosphate (ATP) was first depleted by 2,4-dinitrophenol treatment or anoxia. Only sulfhydryl-blocking agents that enter the cell were effective transport stimulators, and the effect was not altered by substrates of the transporter. In nucleated red blood cell ghosts, NEM inhibited 3-O-methylglucose transport. Results of these studies with intact cells were consistent with the hypothesis that free sulfhydryl groups are essential for regulation of transporter activity rather than for the transport process itself. The locus of NEM action appears to be either on the cytoplasmic side of the membrane or partially located in the cytoplasm. ATP depletion may expose previously masked sulfhydryl groups, producing an enhanced reaction with sulfhydryl-blocking agents and a highly stimulated rate of sugar transport.