Membrane retrieval in the guinea pig neurohypophysis: biochemical characterization of a retrieval structure

Særmark, T.; Jones, Peter M.; Robinson, I. C. A. F.

doi:10.1016/0005-2736(85)90201-9

Cited by 1 publication

(2 citation statements)

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“…At 100 mosm, 87 + 9% (n = 8) of the total amount of 35S was released as labelled neuropeptides. An acid extract of the material bound to the lysed membranes showed that most of the radioactivity remaining membrane-bound was found in the neuropeptides, although SDS/polyacrylamide-gel electrophoresis showed that certain membrane proteins were radiolabelled (Saermark et al, 1985b), but such proteins accounted for less than 10% of the total secretory-vesicle 35S radioactivity. ATPase activity in isolated secretory vesicles…”

Section: Radiolabelling Of Secretory Vesiclesmentioning

confidence: 99%

“…3) (means of two expts.). similar approach, we measured the time-dependent sedimentation of ATPase activity and secretory vesicles on a 800 ,u sucrose gradient (see the Experimental section, and Saermark et al, 1985b). More than 40% of the neurohormones in the starting material (P2) could be sedimented at 1.4 M-sucrose on these gradients after 3 h centrifugation at 100000 gay.…”

Section: Radiolabelling Of Secretory Vesiclesmentioning

confidence: 99%

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Processing and secretion in the neurohypophysis. Stability of isolated secretory vesicles and role of internal pH

Særmark¹,

Andersen²,

Atke³

et al. 1986

Biochemical Journal

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A possible role of low pH in secretory vesicles for processing and secretion in the neurohypophysis was investigated. Subcellular fractionation of guinea-pig neural lobes revealed that a proton present in the membranes from this tissue could not be ascribed to secretory vesicles. However, a proton pump was found in coated microvesicles. Secretory vesicles isolated from rats and guinea pigs were stable under conditions known to lyse secretory vesicles from the adrenal medulla owing to the generation of a proton gradient. These results suggest that the internal pH of secretory vesicles from the neurohypophysis is closer to neutral than is the pH in chromaffin secretory vesicles. Processing of a neurophysin-glycopeptide intermediate from the biosynthesis of vasopressin in intact secretory vesicles incubated in vitro was activated by the addition of NH4Cl, known to increase the intravesicular pH. This activation of neurohormone processing was also apparent in isolated nerve endings incubated in the presence of NH4Cl, suggesting that NH4Cl can also be used to increase the intravesicular pH in intact nerve endings. However, NH4Cl did not affect the secretion of neurohormones, indicating that a low intravesicular pH is not important for exocytosis in the neurohypophysis. Our results indicate that a low pH generated during processing by mechanisms other than ATP-dependent proton transport may inhibit the processing enzymes, thereby preventing extensive breakdown of neurohormone precursors.

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Section: Radiolabelling Of Secretory Vesiclesmentioning

confidence: 99%

Section: Radiolabelling Of Secretory Vesiclesmentioning

confidence: 99%