Klaus H. Hofmann

Klaus H. Hofmann (February 21, 1911 – December 25, 1995) was an American biological chemist and medical researcher.[1][2] The New York Times called Hofmann an "expert on synthesis of body compounds".[1] His career was highlighted by synthesis of a prototype birth control pill, isolation and structural characterization of biotin (vitamin H), determination of the lysine specificity of the pancreatic protease trypsin (an attribute that made it the enzyme of first choice in protein sequence determinations), the first chemical synthesis of a fully biologically-active portion of the peptide hormone (adrenocorticotopic hormone - ACTH),[3] and structure-function studies on ribonuclease (RNase).

Klaus H Hofmann
Hofmann in his laboratory at the University of Pittsburgh, c. 1990
Born(1911-02-21)February 21, 1911
Karlsruhe, Germany
Died(1995-12-25)December 25, 1995
Pittsburgh, Pennsylvania, U.S.
NationalitySwiss

Early life and entry to science

Hofmann was born in Germany but when his father died, his mother returned with her one-year-old son to her family home in Switzerland. The family was business oriented but Klaus was determined to pursue a career in science. He studied steroid chemistry at the Federal Institute of Technology in Zürich (ETH) in the laboratories of Leopold Ružička. Here he developed a friendship with another faculty member, Tadeus Reichstein from whom he learned laboratory technique. For his postdoctoral experience he traveled to the United States to work with Max Bergmann on peptides, an entirely new field for him. From there he migrated across the street to the laboratory of Vincent du Vigneaud where he was introduced to a new vitamin, Biotin.

The war years

What was meant to be a short stay in the US turned into a much longer one as a result of World War II. Switzerland, ringed by hostile forces, advised Hofmann, an officer in the Swiss militia, not to return for the course of the war. He spent the war years working as a guest at Ciba Pharmaceutical Company in New Jersey. From there he moved to the University of Pittsburgh at a time when the institution was trying to build a research reputation.

A scientific home in Pittsburgh

In a few short years, the Dean of the School of Medicine, himself a professor of Biochemistry, invited Hofmann to become Chairman of the Department. From the moment he took the position of Chairman of Biochemistry, it became clear that although he would always be a son of Switzerland, the United States offered him career opportunities he could never hope for in a small country like Switzerland. The US was to become his permanent home. The burgeoning field of peptide chemistry became his scientific focus and, in his own words, he fell in love with a molecule that was known to stimulate the adrenal cortex to produce the very steroids that had so fascinated him in Reichstein's laboratory. That molecule, not yet isolated, was ACTH and the love affair was lifelong. Despite detours into other areas, he kept returning to ACTH. In the last years before his death, he was developing methods to isolate the ACTH receptor.

Areas of scientific accomplishments

Steroid Chemistry

As a PhD student in the laboratories of future Nobel Laureates, Leopold Ruzicka and Tadeus Reichstein in Zürich, Hofmann synthesized a number of compounds related to terpenes, the hypothetical building block of steroids. One of these was a dehydroandrosterone derivative, a prototype for the birth control pill. Unfortunately the biological basis for reproduction was not known for many years subsequent to this and therefore the importance of this compound was not recognized.[4]

Trypsin

While working in the laboratory of Max Bergmann at Rockefeller Institute, now Rockefeller University, Hofmann synthesized analogs of the amino acid lysine and proved that the enzyme trypsin cleaves linkages involving the carboxyl group of that amino acid.[5]

Biotin

Subsequently, with Vincent du Vigneaud, he used the newly developed technique of chromatography that he had learned while a student in Zürich, to isolate and then crystallize biotin.[6][7] This work began a theme that continued throughout his career of determining the importance of sulfur [8][9] in biologically active structures. He applied this to peptides as well.

Peptide synthesis/ACTH

The first chemical synthesis of an active peptide hormone, the nine amino acid cyclic peptide, oxytocin, was achieved in 1954 by du Vigneaud[10] for which he was awarded the Nobel Prize. At the same time, the isolation and structure determination of the anterior pituitary hormone, ACTH, was being pursued in three laboratories.[11][12][13] The peptide was eventually determined to be 39 amino acids in length, however enzymatic and mild acid cleavage[14] suggested that a structure comprising only the first 24 amino acids had full biological activity. It was apparent from the outset that ACTH contained the amino acid Arginine and thus methods had to be developed for the incorporation of this basic amino acid into peptides. Hofmann and his group set about this task.[15] Their efforts led to the synthesis of the melanocyte stimulating hormone, β-MSH, which corresponds to the first 13 amino acids of ACTH [16] and to the synthesis of a fully active ACTH peptide corresponding to the amino acid sequence of the first 23 amino acids.[17]

In the course of the peptide synthetic work on ACTH, a novel chain cleavage was observed at an acyl-proline linkage while removing protecting groups using metallic sodium in liquid ammonia.[18] This unexpected reaction has subsequently proved useful in special analytical cases.[19]

RNaseA

In 1959, Fred Richards discovered that a proteolytic enzyme, Subtilisin, had the ability to cleave the enzyme Ribonuclease A into two components, a peptide corresponding to the first 20 amino acids of the enzyme (S-Peptide) and the remainder of the protein (S-Protein).[20] When separated from one another, each piece was inactive but when they were simply mixed together, full enzymatic activity was restored. Hofmann speculated that this system might be a model for the way peptide hormones interact with their receptors.[21] Structure-function studies with ACTH were complicated by the necessity to assess activity in the whole animal. The S-Peptide:S-Protein system afforded a simple system with none of the biological complications inherent in testing ACTH analogs.

To study which amino acids might be important in establishing the binding between peptide hormones and their receptors, Hofmann and his group began a systematic evaluation of the contributions each amino acid in the S-Peptide molecule made to the binding with S-Protein. The ability of synthetic analogs of S-Peptide to activate S-Protein correlated well with those of synthetic ACTH analogs to elicit hormonal activity: 1) only a portion of the S-Peptide chain was essential for re-establishing full activity [22] with the S-Protein; 2) methionine was not important;[23] 3) substituting one particular amino acid in the peptide not only destroyed the activity of the peptide but created an antagonist as well.[24][25] Once it was established that peptide hormone receptors resided on the plasma membrane of cells, direct studies of the activity of ACTH derivatives that had so long eluded researchers finally became a reality. Hofmann and his colleagues isolated plasma membranes from beef adrenals[26] and were able to conduct structure-activity studies with synthetic analogs of ACTH. Importantly they found that substituting Phenylalanine for theTryptophan residue in position 9 produced a peptide that bound to the ACTH receptor without activating it, i.e. and ACTH antagonist.[27][28]

Return to Biotin receptor isolation

Hofmann came full circle to his early work on biotin when he attached this vitamin to insulin. He spent a sabbatical leave in Aachen in Helmut Zahn's laboratory to learn techniques for modifying insulin[29]). Using this information, he was able to chemically attach biotin to one of the three Lys residues of the insulin chains, thus producing an insulin that would bind to columns of avidin-Sepharose. The biotinyl-insulin receptor complex could then be displaced by biotin. With this tool, Hofmann and his coworkers successfully isolated a fully active insulin receptor.[30] His final work was directed toward isolation of the ACTH receptor using the same approach used on the insulin receptor but by this time his health was in decline.

Distinctions

Hofmann was the founder and the director of Protein Research Laboratory at the School of Medicine at University of Pittsburgh,[1][31] a member of the National Academy of Sciences,[1][2] Professor Emeritus of Experimental Medicine and Biochemistry at the University of Pittsburgh School of Medicine,[1] and a member of American Association for the Advancement of Science.[2]

Awards and distinctions

Hofmann was a member of:

Hofmann was recognized with the following awards:

  • 1962 Pittsburgh Award[2]
  • 1963 Election to membership in the National Academy of Sciences[2]
  • 1963 Borden Medal[2]
  • 1963 Chancellors Medal, University of Pittsburgh[2]
  • 1972 Mellon Lecture, University of Pittsburgh[2]
  • 1976 Senior Scientist Award, Alexander Von Humboldt Foundation, Bonn, West Germany[2]
  • 1981 Third Alan E. Pierce Award by the American Peptide Chemists[2]
  • 1983 Japan Society for the Promotion of Sciences Fellowship Award[2]
  • 1987 First Huggins Memorial Award, University of Pittsburgh[2]

References
  1. New York Times:K. H. Hofmann, 84, Expert on Synthesis Of Body Compounds, By WOLFGANG SAXON, December 28, 1995
  2. National Academies Press:Biographical Memoirs V.81 (2002), KLAUS HOFMANN, BY FRANCES M. FINN AND BERT W. O’MALLEY
  3. New York Times:Scientists Synthesize Substance Biologically Equal to ACTH; Molecule Has 23 Amino Acids Against Nature's 39 -- Aid to Pituitary Study Is Seen SCIENTISTS MAKE ACTH SUBSTITUTE;By WALTER SULLIVAN, December 02, 1960
  4. Ruzicka, L and Hofmann, K. Zur Kenntnis von 17-Athinyl- und 17-Vinyl-androstan.-androsten-Derivaten und deren Oxydationsprodukten. Helv. Chim Acta 22 150-155 1939.
  5. Hofmann, K and Bergmann, M. The Specificity of Trypsin. II. J. Biol. Chem. 130 81-86 1939.
  6. du Vigneaud, V., Hofmann, K., Melville, D. B. and György, P. Isolation of Biotin (Vitamin H) from Liver. J. Biol. Chem. 140 643-651 1941.
  7. du Vigneaud, V., Hofmann, K., Melville, D. B. and Rachele, J. R. The Preparation of Free Crystalline Biotin. J. Biol. Chem. 140 763-766 1941.
  8. Hofmann, K. Furan and Tetrahydrofuran Derivatives. VI The Total Synthesis of dl-Oxybiotin J. Am. Chem. Soc. 67 1459-1462 1945.
  9. Hofmann, K., Chen, C., Bridgwater, A. and Axelrod, A. E. Furan and Tetrahydrofuran Derivatives VII. The Synthesis and Biological Actiity of a Number of Oxybiotin Homologs. J. Am. Chem. Soc. 69 191-195 1947.
  10. du Vigneaud, V. Ressler, C. Swan, J. M. Roberts, C. W. and Katsoyannis, P. G. The Synthesis of Oxytocin. J. Am. Chem Soc. 76 3115-21 1954.
  11. Bell, P. H. Purification and Structure of β-corticotropin. J. Am. Chem. Soc. 76 5565-67 1954.
  12. Li, C. H., Geschwind, I. I., Levy, A. L., Harris, J. I. Dixon, J. S., Pon, N. G., and Porath, J. O. Amino-Acid Sequence of Alpha-Corticotropin. Nature 173 251 1954.
  13. White, W. F. and Landmann, W. A. Studies on Adrenocorticotropin XI. A Preliminary Comparison of Corticotropin-A with β-Corticotropin. J. Am. Chem. Soc. 77 1711 1955.
  14. 11. Brink, N. G., Kuehl, F. A. Richter, J. W. Bazemore, A. W., Meisinger, M. A. P. Ayer, D. E. and Folkers, K. Pituitary Hormones III. The isolation of Corticotropin-B. J. Am. Chem. Soc. 74 2120-21 1952.
  15. Hofmann, K, Rheiner, A. and Peckham, W. D. Studies on Polypeptides. V. The Synthesis of Arginine Peptides. J. Am. Chem. Soc. 75 6083 1953.
  16. Hofmann, K and Yajima, H. Studies on Polypeptides. XX. Synthesis and Corticotropic Activity of a Peptide Amide Corresponding to the N-Terminal Tridecapeptide Sequence of the Corticotropins. J. Am. Chem. Soc. 83 2289-93 1961.
  17. Hofmann, K., Yajima, H., Yanaihara, N., Liu, T-Y, and Lande, S. Studies on Polypeptides. XVIII. The Synthesis of a Tricosapeptide Possessing Essentially the Full Biological Activity of Natural ACTH J. Am. Chem. Soc. 83 487-89 1961.
  18. Hofmann, K., Yajima, H. Studies on Polypeptides. XX. Synthesis and Corticotropic Activity of a Peptide Amide Corresponding to the N-Terminal Tridecapeptide Sequence of the Corticotropins J. Am. Chem. Soc. 83, 10, 2289–2293, 1961 Publication Date:May 1, 1961 https://doi.org/10.1021/ja01471a017
  19. Hempel, J., Jörnvall, H. Cleavage at Acyl-Proline Bonds With Sodium in Liquid Ammonia: Application With Nanomolar Amounts of Peptides and Separation of Products by High-Performance Liquid Chromatography for Structural Analysis. Anal. Biochem.. Dec;151(2):225-30, 1985 https://doi.org/10.1016/0003-2697(85)90169-1.
  20. Richards, F. M. and Vithayathil, P. J. The Preparation of Subtilisin-modified Ribonuclease and the Separation of the Peptide and Protein Components. J. Biol. Chem. 234 1459-65 1959.
  21. Hofmann, K. Preliminary Observations Relating Structure and Function in Some Pituitary Hormones. Brookhaven Symposia in Biology 13 184-202 1960.
  22. Hofmann, K., Finn, F. M., Limetti, M., Montibeller, J., and Zanetti, G. Studies on Polypeptides. XXXIV. Enzymic Properties of Partially Synthetic De(16-20)- and De(15-20)-ribonucleases S’, J. Am. Chem. Soc. 88 3633-39 1966
  23. Finn, F. M. and Hofmann, K. Studies on Polypeptides XXXIII. Enzymic Properties of Partially Synthetic Ribonucleases. J. Am. Chem. Soc. 87 645-51 1965.
  24. Hofmann, K. and Bohn, H. Studies on Polypeptides. XXXVI. The Effect of Pyrazole-Imidazole Replacements on the S-Protein Activating Potency of an S-Peptide Fragment. J. Am. Chem. Soc. 88 5914-19 1966.
  25. Hofmann, K., Bohn, H., Andreatta, R. and Moroder, L. Studies on Polypeptides XLV. Structure-Function Studies in the ß-Corticotropin Series. J. Am. Chem. Soc. 89 7126-27 1967.
  26. Finn, F. M. Widnell, C. C. and Hofmann, K. Localization of an Adrenocorticotropic Hormone Receptor on Bovine Adrenal Cortical Membranes. J. Biol. Chem. 247 5695-5702 1972.
  27. Hofmann, K., Wingender, W. and Finn, F. M. Correlation of Adrenocortocotropic Activity of ACTH Analogs with Degree of Binding to an Adrenal Cortical Particulate Preparation. Proc. Natl. Acad. Sci. 67 829-36 1970.
  28. Hofmann, K., Montibeller, J. A. and Finn, F. ACTH Antogonists. Proc. Natl. Acad. Sci. 71 80-83.
  29. Hofmann, K., Finn, F. M., Friesen, H-J., Diaconescu, C. and Zahn, H. Biotinylinsulins as potential tools for receptor studies, Proc. Natl. Acad. Sci. 74 2697-2700 1977.
  30. Finn, F. M., Titus, G., Horstman, D. and Hofmann, K. Avidin-biotin affinity chromatography: application to the isolation of human placental insulin receptor. Proc. Natl. Acad. Sci. 81 7328-32 1984.
  31. New York Times:Chinese Synthesize Insulin, German Scientists Confirm; Medical Value Cited Chinese Synthesis of Insulin Proved British Study Noted by WALTER SULLIVAN, September 12, 1966
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