Uptake and intracellular fate of [14C]sucrose-insulin in perfused rat livers

C. A. Surmacz, J. J. Wert, W. F. Ward, G. E. Mortimore

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Abstract

Insulin was covalently linked to [14C]sucrose by means of cyanuric chloride to provide a label that would remain entrapped within the vacuolar system. The uptake of the conjugate by the perfused rat liver was rapid (half-life = 2.9 min), competitively inhibited by native insulin, and abolished by alkali denaturation. As assessed by its distribution on self-generating gradients of colloidal silica-povidone, label in lysosome-enriched samples of liver taken at different times after the addition of the conjugate moved progressively during 15 min from the plasma membrane into an intermediate peak and then to dense lysosomal fractions. After 30-60 min, the label had equilibrated throughout the lysosomal-vacuolar system. The initial movement from the plasma membrane to the intermediate peak occurred between 2 and 5 min. Because label in the peak could be physically separated from the lysosomal marker, β-acetylglucosaminidase, by dispersing the sample through the gradient mixture before centrifugation rather than layering it, we concluded that the intermediate particles in question were not lysosomal in nature. On gel-filtration chromatography, label extracted from the intermediate peak did not move with insulin but rather as a broad band of lower molecular weight products, suggesting that insulin is subject to early proteolytic attack within a nonlysosomal compartment.

Original languageEnglish (US)
Pages (from-to)24/1
JournalAmerican Journal of Physiology - Cell Physiology
Volume255
Issue number1
StatePublished - Jan 1 1988

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ASJC Scopus subject areas

  • Physiology
  • Cell Biology

Cite this

Surmacz, C. A., Wert, J. J., Ward, W. F., & Mortimore, G. E. (1988). Uptake and intracellular fate of [14C]sucrose-insulin in perfused rat livers. American Journal of Physiology - Cell Physiology, 255(1), 24/1.