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Khorana, Har Gobind (1922- )

Khorana, Har Gobind (1922- )

Indian-born American biochemist

Har Gobind Khorana, an organic chemist who specialized in the study of proteins and nucleic acids, shared the Nobel Prize in Physiology of Medicine with Robert W. Holley (1922 ) and Marshall W. Nirenberg (1927 ) in 1968 for discoveries related to the genetic code and its function in protein synthesis . In addition to developing methods for investigating the structure of the nucleic acids, Khorana introduced many of the techniques that allowed scientists to decipher the genetic code and show how ribonucleic acid (RNA ) can specify the structure of proteins. Four years after winning the Nobel Prize, Khorana succeeded in synthesizing the first wholly artificial gene . In the 1980s Khorana synthesized the gene for rhodopsin, a protein involved in vision.

Har Gobind Khorana, youngest of the five children of Shri Ganput Rai Khorana and Shrimat Krishna Devi Khorana, was born in Raipur, in the Punjab region of India (now part of West Pakistan). His birth date was recorded as January 9, 1922, but the exact date of his birth is uncertain. Although his family was poor, his parents believed strongly in the importance of education. His father was a village agricultural taxation clerk in the British colonial government. Khorana attended D.A.V. High School in Multan (now West Punjab). After receiving his Bachelor of Science (1943, with honors) and Master's degree (1945, with honors) from Punjab University in Lahore, India, Khorana was awarded a Government of India Fellowship, which enabled him to study at Liverpool University, England, where he earned his Ph.D. in 1948. From 1948 to 1949, he worked as a postdoctoral fellow at the Federal Institute of Technology, Zurich, Switzerland, with Professor Vladimir Prelog, who had a major influence on his life-long approach to science.

After briefly returning to India, Khorana accepted a position in the laboratory of (Lord) Alexander Todd at Cambridge University (195052), where he studied proteins and nucleic acids. From 1952 to 1960, Khorana worked in the organic chemistry section of the British Columbia Research Council, Vancouver, Canada. The next year Khorana moved to the University of Wisconsin, Madison, Wisconsin, where he served as Co-director of the Institute for Enzyme Research and Professor of Biochemistry . In 1964, he became the Conrad A. Elvehjem Professor of the Life Sciences. In 1970, Khorana accepted the position of Alfred P. Sloan Professor, Departments of Biology and Chemistry, at the Massachusetts Institute of Technology, Cambridge, Massachusetts. From 1974 to 1980, he was Andrew D. White Professor-at-large, Cornell University, Ithaca, New York. During his long and distinguished career, Khorana has been the author or co-author of over 500 scientific publications.

In 1953, Khorana and Todd published their only coauthored paper; it described the use of a novel phosphorylating reagent. Khorana found that this reagent was very useful in overcoming problems in the synthesis of polynucleotides. Between 1956 and 1958, Khorana and his coworkers established the fundamental techniques of nucleotide chemistry. Their goal was to develop purely chemical methods of synthesizing oligonucleotides (long chains of nucleotides). In 1961, Khorana synthesized Coenzyme A, a factor needed for the activity of certain key metabolic enzymes .

In 1955, Khorana learned about Severo Ochoa's discovery of the enzyme polynucleotide phosphorylase and met Arthur Kornberg, who described pioneering research on the enzymatic synthesis of DNA . These discoveries revolutionized nucleic acid research and made it possible to elucidate the genetic code. Khorana and his coworkers synthesized each of the 64 possible triplets (codons) by synthesizing polynucleotides of known composition. Khorana also devised the methods that led to the synthesis of large, well-defined nucleic acids.

By combining synthetic and enzymatic methods, Khorana was able to overcome many obstacles to the chemical synthesis of polyribonucleotides. Khorana's work provided unequivocal proof of codon assignments and defined some codons that had not been determined by other methods. Some triplets, which did not seem to code for any particular amino acid, were shown to serve as "punctuation marks" for beginning and ending the synthesis of polypeptide chains (long chains of amino acids). Khorana's investigations also provided direct evidence concerning other characteristics of the genetic code. For example, Khorana's work proved that three nucleotides specify an amino acid, provided proof of the direction in which the information in messenger RNA is read, demonstrated that punctuation between codons is unnecessary, and that the codons did not overlap. Moreover, construction of specific polyribonucleotides proved that an RNA intermediary is involved in translating the sequence of nucleotides in DNA into the sequence of amino acids in a protein. Summarizing the remarkable progress that had been made up to 1968 in polynucleotide synthesis and understanding the genetic code, Khorana remarked that the nature of the genetic code was fairly well established, at least for Escherichia coli.

Once the genetic code had been elucidated, Khorana focused on gene structure-gene function relationships and studies of DNA-protein interactions. In order to understand gene expression, Khorana turned to DNA synthesis and sequencing. Recognizing the importance of the class of ribonucleotides known as transfer RNAs (tRNAs), Khorana decided to synthesize the DNA sequence that coded for alanine tRNA. The nucleotide sequence of this tRNA had been determined in Robert Holley's laboratory. In 1970, when Khorana announced the total synthesis of the first wholly artificial gene, his achievement was honored as a major landmark in molecular biology . Six years later, Khorana and his associates synthesized another gene. In the 1980s, Khorana carried out studies of the chemistry and molecular biology of the gene for rhodopsin, a protein involved in vision.

In 1966, Khorana was elected to the National Academy of Sciences. His many honors and awards include the Merck Award from the Chemical Institute of Canada, the Dannie-Heinneman Prize, the American Chemical Society Award for Creative Work in Synthetic Organic Chemistry, the Lasker Foundation Award for Basic Medical Research, the Padma Vibhushan Presidential Award, the Ellis Island Medal of Honor, the National Medal of Science, and the Paul Kayser International Award of Merit in Retina Research. He holds Honorary Degrees for numerous universities, including Simon Fraser University, Vancouver, Canada; University of Liverpool, England; University of Punjab, India; University of Delhi, India; Calcutta University, India; University of Chicago; and University of British Columbia, Vancouver, Canada.

See also Genetic regulation of eukaryotic cells; Microbial genetics

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Har Gobind Khorana

Har Gobind Khorana

Har Gobind Khorana (born 1922) was an Indian organic chemist and cowinner of the 1968 Nobel Prize for physiology or medicine. His research in chemical genetics vastly extended our understanding of how the chemicals of a cell nucleus transmit information to succeeding generations of cells.

Har Gobind Khorana was born in Raipur on January 9, 1922. After obtaining a doctorate in chemistry from the University of Liverpool, he worked with V. Prelog at the Federal Institute of Technology in Zurich and with Sir Alexander Todd at Cambridge University. From 1952 to 1960 he was head of the Organic Chemistry Group of the British Commonwealth Research Council in Vancouver, and for part of this period he was visiting research professor at the Rockefeller University in New York City. He moved to the University of Wisconsin in 1960 and in 1964 was named to the Conrad A. Elvehjem chair in life sciences at the Institute of Enzyme Research.

Khorana's research embraced many fields: peptides and proteins; chemistry of phosphate esters, nucleic acids, and viruses; and chemical genetics. It was his work in chemical genetics that secured for him three coveted prizes: the Merck Award of the Chemical Institute of Canada in 1958, the Louisa Gross Horwitz Prize of Columbia University in 1968, and the Nobel Prize in the same year.

Khorana's work supplements the research of Marshall Nirenberg and Robert Holley. In 1961, while experimenting with the intestinal bacterium Escherichia coli, Nirenberg had deciphered the coded messages that DNA (deoxyribonucleic acid) sends to RNA (ribonucleic acid), which in turn prescribes the synthesis of new proteins. Further experiments revealed codes for most of the known amino acids normally present in proteins. But, although the nucleotide composition became known, gaps in the knowledge about the order of the nucleotide remained.

With his coworkers Khorana resolved this gap by synthesizing all of the 64 possible trinucleotides. He used synthetic polydeoxyribonucleotides of known sequence to direct the synthesis of long, complementary, polyribonucleotides in reactions catalyzed by the enzyme RNA polymerase. By preparing RNA-like polymers with alternating sequence, he demonstrated that such a polymer directs the synthesis of a polypeptide with alternating amino acids—leucine and serine.

After testing a large number of such polymers, Khorana afforded a clear proof of codon assignments and confirmed that the genetic language is linear and consecutive and that three nucleotides specify an amino acid. In addition, he proved the direction in which the information of the messenger RNA is read and that the code words cannot overlap. The manner in which polyribonucleotides are manufactured afforded the clearest proof that the sequence of nucleotides in DNA specifies the sequence of amino acids in proteins through the intermediary of an RNA.

In 1970 Khorna left the University of Wisconsin for the Massachusetts Institute of Technology, becoming the Alfred P. Sloan Professor. He was associated with Cornell University from 1974 to 1980 as well. Also in 1970, Khorana made a major breakthrough when he announced the synthesis of the first artificial gene. Six years later, Khorana and his team created a second artificial gene, this one capable of functioning in a living cell. This valuable work laid the foundation for a future in which scientists could use artificial genes to synthesize important proteins or to cure hereditary diseases in humans. In recent years, Khorana has synthesized the gene for bovine rhodopsin, the retinal pigment that converts light energy into electrical energy.

Khorana, who became an American citizen in 1966, has developed a reputation as a tireless worker who once went 12 years without a vacation. He enjoys hiking, listening to music, and often takes his scientific inspiration from long daily walks. With his wife, Esther Elizabeth Sibler, he raised two daughters, Julia Elizabeth and Emily Anne, and one son, Dave Roy.

Further Reading

An autobiographical sketch by Khorana, his Nobel lecture, and the presentation speech of the Nobel Committee (all in English) appear in the annual Les Prix Nobel en 1968 (1969). A good source for understanding genetical research and Khorana's work is Robert H. Haynes and Philip C. Hanawalt, eds., The Molecular Basis of Life: An Introduction to Molecular Biology (1968). His work is also discussed in Carl R. Woese, The Genetic Code: The Molecular Basis for Genetic Expression (1967). □

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Khorana, Har Gobind

Khorana, Har Gobind


AMERICAN BIOCHEMIST 1922

Har Gobind Khorana was born in a small village in British India, in which his family was among the few literate residents. He received his M.S. from the University of Lahore, and in 1945 he was awarded a grant to study for a Ph.D. at the University of Liverpool. He then went on to complete postdoctoral work in Switzerland and at Cambridge. It was there, while working with Alexander Todd, that Khorana became interested in both nucleic acids and proteins, the study of which became his life's work.

In 1952 G. M. Shrum, head of the British Research Council on the campus of the University of British Columbia, Vancouver, Canada, offered Khorana the opportunity to form his own research group on whatever topic he wished. His group became very successful in developing methods for synthesizing phosphate ester derivatives of nucleic acids, and in 1959 he and John G. Moffatt announced the synthesis of acetyl coenzyme A (acetyl CoA), a molecule essential to the biochemical processing of proteins fats and carbohydrates. Prior to this work, the coenzyme had to be extracted from yeast by a very laborious and expensive process, so this discovery led to Khorana's international recognition within the scientific community and he received many job offers as a result. He accepted the position of codirector of the Institute for Enzyme Research at the University of Wisconsin.

In the early 1960s it had been recognized that DNA and RNA (in the form of messenger RNA [mRNA]) were somehow involved in the synthesis of proteins in living cells. Whereas the basic building blocks of DNA are the four nucleotides adenosine (A), cytosine (C), guanine (G), and thymine (T)in RNA, uracil (U) is substituted for thiaminethe basic building blocks of all proteins are twenty amino acids strung together in different sequences to produce individual proteins. In 1961, Marshall W. Nirenberg, and Heinrich J. Matthaei announced that they had created a synthetic mRNA, which, when inserted into E. coli bacteria, always caused the addition of one amino acid phenylalanine to a growing strand of linked amino acid. They also determined that if they synthesized RNA with three units of uracil joined together, it caused an amino acid chain consisting entirely of phenylalanine to be produced.

These experiments, which proved that mRNA transmits the genetic information from DNA, thus directing the creation of specific complex proteins, stimulated Khorana to use his expertise in polynucleotide synthesis to uncover the exact mechanisms involved. The results were spectacular. Within a few short years his research group was able to establish which serial combinations of nucleotides form which specific amino acids; that nucleotide instructions (genetic code ) are always transmitted to the cell in groups of three called codons; and that some of the codons direct the cell to start or stop the manufacture of proteins. For this work Khorana, along with Nirenberg and biochemist Robert W. Holley, was awarded the Nobel Prize in physiology in 1968.

In 1970 Khorana announced the creation of the first artificial DNA gene of yeast. At the same time, he and most of his research team moved to the Massachusetts Institute of Technology (MIT) because, as he explained, "You stay intellectually alive longer if you change your environment every so often" (McMurray, p. 1089). Since going to MIT, Khorana has reported major advances concerning how rhodopsin, the photo receptor in the human eye, functions.

see also Codon; Nucleic Acids; Todd, Alexander.

John E. Bloor

Bibliography

McMurray, Emily J., ed. (1995). Notable Twentieth-Century Scientists. Detroit, MI: Gale Research.

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Khorana, Har Gobind

Har Gobind Khorana, 1922–, American biochemist, b. Raipur (now in Pakistan), Ph.D. Univ. of Liverpool, 1948. He became a U.S. citizen in 1966, and has been a professor at the Massachusetts Institute of Technology since 1970. Khorana, Marshall W. Nirenberg, and Robert W. Holley were awarded the 1968 Nobel Prize in physiology or medicine for their discoveries concerning the genetic code and its function in protein synthesis. Khorana confirmed Nirenberg's finding that the arrangement of the four types of nucleotides on the DNA molecule (see nucleic acid) determines the chemical composition and function of new cells; he then built on this finding and determined the nucleotide combinations that form specific amino acids. Khorana was also the first scientist to synthesize strings of nucleotides.

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