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Joined 2026-09-21 Message
Incoming links: Günter Blobel
By David D. Sabatini, Günter Blobel. Journal of Cell Biology 45(1), 146–157 (1970); published 1 April 1970. Semantic Scholar hosts this journal scan. The byline gives D. D. Sabatini and G. Blobel; the full names are independently verified.
Cited passages: Full original PDF pp. 146–157; Methods p. 147: rat-liver preparation, sucrose centrifugation and Philips EM 300 electron microscope; Activity control p. 148: free polysomes with/without microsomes; Figure 5C–D and text p. 152: chromatography and digestion with membrane-solubilizing detergents; Discussion pp. 155–156: membrane-protected versus ribosome-protected fragments.
By Günter Blobel. Proceedings of the National Academy of Sciences of the United States of America 77(3), 1496–1500 (1980). PubMed Central hosts the record. Only the abstract was inspected.
Inspected record: pmc.ncbi.nlm.nih.gov/articles/PMC348522/
Cited passage: abstract.
Microsomal protein import experiment 2026-10-18
In 1975, Günter Blobel and Bernhard Dobberstein combined cell-free translation with dog-pancreas microsomes. Density-gradient centrifugation isolated the membranes; removal of resident ribosomes allowed reconstitution with rabbit-reticulocyte ribosome subunits. Added messenger RNA encoded an immunoglobulin light chain; globin provided a comparison. Products made with or without membranes were challenged with proteases and analyzed by SDS-PAGE and autoradiography. Membranes present during synthesis yielded processed, protected light chain; globin remained susceptible. Adding membranes after precursor synthesis failed to reproduce import. These comparisons support selective passage during synthesis in this preparation.[ref]
The companion paper specifies radioactive amino acid incorporation, ice-cold trypsin plus chymotrypsin treatment, a slab-gel electrophoresis apparatus and dried-gel exposure to X-ray film. Product-size analysis distinguishes a preserved full-size product from residual labeled fragments.[ref]
Transfer of Proteins across Membranes I by Günter Blobel and Bernhard Dobberstein. Methods pp. 837–838: proteolysis, SDS-PAGE and autoradiography; Discussion p. 847
Protection was incomplete. The authors considered leaky vesicles, and warned that heat treatment could damage processing as well as ribosome attachment. Their experiments did not identify SRP or the Sec61 complex. Nor does failure of late membrane addition establish that all organelle protein import must occur during synthesis.[ref]
Transfer of Proteins across Membranes II by Günter Blobel and Bernhard Dobberstein. pp. 858–859: incomplete protection; p. 861: heat-inactivation caveat; p. 862: alternatives for failed processing
Protease protection assay 2026-10-18
A protease protection assay asks whether a barrier prevents an added protease from reaching a protein. A membrane-disruption comparison tests whether protection depends on that barrier.
Protease protection assay: accessibility and control logic
. Original qualitative decision diagram for a completed soluble cargo. Icons and words describe expected outcomes under stated assumptions; they are not an autoradiography readout, copied historical lanes, measured survival fractions or simulated experimental intensities. Detergent is added after the import reaction. The historical nascent chain experiment also retained small ribosome-protected fragments, which this completed-cargo model deliberately distinguishes. Details.
The membrane-disruption test was performed by David D. Sabatini and Günter Blobel in 1970. Rat-liver microsomes purified by sucrose centrifugation incorporated radioactive leucine during cell-free translation. Samples received cold trypsin and chymotrypsin, with or without membrane-solubilizing detergents. Electron microscopy checked vesicle preservation; size-exclusion chromatography separated protected fragment sizes. Large membrane-associated fragments lost protection after disruption, whereas small ribosome-protected fragments persisted. An exposed ribosome preparation remained digestible when mixed with microsomes, checking that membranes did not simply inhibit the proteases.[ref]
Controlled Proteolysis of Nascent Polypeptides in Rat Liver Cell Fractions II by David D. Sabatini and Günter Blobel. Controlled proteolysis of nascent polypeptides in rat liver cell fractions. II, Methods p. 147; activity control p. 148; Figure 5C–D and text p. 152; Discussion pp. 155–156
To read the qualitative diagram, first compare untreated aliquots: they establish that detectable cargo exists before digestion. Next compare external protease with intact versus disrupted membranes. Persistence only while the barrier remains intact supports enclosure, provided the exposed-cargo control confirms active protease in both chemical conditions. The detergent-only aliquot checks that disruption itself does not destroy recovery or detection. Adding membranes after synthesis tests a different alternative: capture of a completed product rather than entry during biological translation.
This is an argument from controlled accessibility. Binding predicts membrane association but generally leaves an exposed cargo digestible. Enclosure predicts protection that depends on membrane integrity. However, protein aggregation, intrinsic resistance to proteolysis, inactive protease or undetected small fragments can obscure this distinction. For a transmembrane protein, expect protection of the enclosed portion rather than necessarily the full chain. Combine fragment size, compartment controls and membrane topology; a protected signal alone does not uniquely specify the whole protein's location.
Signal peptide 2026-10-18
A signal peptide is a short targeting segment of a newly made polypeptide chain. A familiar ER signal sequence lies near the N-terminus and is removed during entry; Günter Blobel and Bernhard Dobberstein's 1975 experiments linked a larger immunoglobulin light chain precursor to a processed product.[ref]
Transfer of Proteins across Membranes I by Günter Blobel and Bernhard Dobberstein. Transfer of proteins across membranes. I, Introduction p. 836; Figures 5 and 14; Discussion pp. 845–847
Cleavage is a separate question from recognition. Not every targeting signal is a cleaved signal peptide: an internal signal anchor can remain part of a transmembrane protein. Conversely, loss of a segment does not by itself prove membrane crossing. Compare the independent size and accessibility readouts in the microsomal protein import experiment.
By Günter Blobel, Bernhard Dobberstein. Journal of Cell Biology 67(3), 835–851 (1975). The University of California, Berkeley hosts this journal scan.
Inspected text: mcb.berkeley.edu/labs/krantz/pdf/blobel%26dobberstein-transfer_of_proteins_across_membranes_I-JCB-1975.pdf
Cited passages: Introduction p. 836; Methods pp. 837–838: cell-free translation, proteolysis, slab SDS-PAGE and dried-gel autoradiography; Figures 5,7,14; Discussion p. 847: size-resolved protection versus sedimentation.
By Günter Blobel, Bernhard Dobberstein. Journal of Cell Biology 67(3), 852–862 (1975). SciSpace hosts this journal scan.
Inspected text: scispace.com/pdf/transfer-of-proteins-across-membranes-ii-reconstitution-of-5pau33unje.pdf
Cited passages: Methods p. 853: dog-pancreas microsomes, centrifugation, stripped preparations; Figure 6 and text pp. 856–859: light chain, globin, plus/minus protease; Figure 7 and text pp. 860–861: reconstitution and heat-inactivation caveat; Figure 8 and text pp. 861–862: membranes after synthesis, failed detergent-solubilized processing.