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A pathway for secretion

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Littlefield et al. (1955) made a promising start by showing that radioactive amino acids accumulated first in the detergent-resistant particles of the microsomes (i.e., the ribosomes) before moving into the membranous portion... The authors felt confident to state that “the cytoplasmic ribonucleoprotein particles are the site of initial incorporation of free amino acids into protein. ”Siekevitz and Palade (1958) came to a similar conclusion, and extended the work to show that the label continued on from the microsome fraction to reach the pancreatic zymogen granules... The Golgi had been destroyed by the earlier biochemical fractionations, so this was its first appearance in the pathway... Jamieson and Palade (1967a,b) used in vitro tissue slices so that pulse times could be more precisely controlled; thus they demonstrated that there was indeed a flow of protein from one compartment to the next... As the autoradiography became more exact, Jamieson and Palade (1971) could also conclude that the proteins were inside rather than outside the Golgi cisternae, and thus the proteins were not traveling through the cytoplasm as some had suggested. “The evidence was overwhelming” for this basic secretory pathway, says Siekevitz, and it was generally accepted... These early results from studies with secretory cells had turned up a model that was good at explaining secretion... But the story of protein synthesis itself remained incomplete—not least because of the inexact nature of biochemical fractionation. “Even with the corrections envisaged,” said Siekevitz and Palade (1958), “…it seems unlikely that the decrease in microsomal radioactivity [over time] could balance the increase in counts in all the other cell fractions... It follows that incorporation of amino acids into proteins, and presumably protein synthesis, is not necessarily restricted to microsomes. ” The other half of the equation was not filled in until the report of Ganoza and Williams (1969)... They made the correlation between, on the one hand, membrane-bound ribosomes that made secreted proteins and, on the other, nonmembrane-bound ribosomes that made nonsecreted proteins.

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Labeled proteins start off in the ER.PALADE
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uro2: Labeled proteins start off in the ER.PALADE


A pathway for secretion
Labeled proteins start off in the ER.PALADE
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2254713&req=5

uro2: Labeled proteins start off in the ER.PALADE

View Article: PubMed Central

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

Littlefield et al. (1955) made a promising start by showing that radioactive amino acids accumulated first in the detergent-resistant particles of the microsomes (i.e., the ribosomes) before moving into the membranous portion... The authors felt confident to state that “the cytoplasmic ribonucleoprotein particles are the site of initial incorporation of free amino acids into protein. ”Siekevitz and Palade (1958) came to a similar conclusion, and extended the work to show that the label continued on from the microsome fraction to reach the pancreatic zymogen granules... The Golgi had been destroyed by the earlier biochemical fractionations, so this was its first appearance in the pathway... Jamieson and Palade (1967a,b) used in vitro tissue slices so that pulse times could be more precisely controlled; thus they demonstrated that there was indeed a flow of protein from one compartment to the next... As the autoradiography became more exact, Jamieson and Palade (1971) could also conclude that the proteins were inside rather than outside the Golgi cisternae, and thus the proteins were not traveling through the cytoplasm as some had suggested. “The evidence was overwhelming” for this basic secretory pathway, says Siekevitz, and it was generally accepted... These early results from studies with secretory cells had turned up a model that was good at explaining secretion... But the story of protein synthesis itself remained incomplete—not least because of the inexact nature of biochemical fractionation. “Even with the corrections envisaged,” said Siekevitz and Palade (1958), “…it seems unlikely that the decrease in microsomal radioactivity [over time] could balance the increase in counts in all the other cell fractions... It follows that incorporation of amino acids into proteins, and presumably protein synthesis, is not necessarily restricted to microsomes. ” The other half of the equation was not filled in until the report of Ganoza and Williams (1969)... They made the correlation between, on the one hand, membrane-bound ribosomes that made secreted proteins and, on the other, nonmembrane-bound ribosomes that made nonsecreted proteins.

No MeSH data available.