Russian–American biochemist (1869–1940)
Levene was born in Sagor, Russia, and gained his MD from St. Petersburg in 1891. He then emigrated with his family to America where he attended courses in chemistry at Columbia University, New York. He continued his chemical studies in Germany under Emil Fischer and Albrecht Kossel, who introduced him to the study of nucleic acids. In 1905 he joined the newly formed Rockefeller Institute for Medical Research where he remained for the rest of his career.
It was known that nucleic acid exists in two forms, one found in the thymus of animals and the other in yeast. Kossel had shown that thymus nucleic acid contained the four nitrogen compounds adenine, guanine, cytosine, and thymine, whereas yeast nucleic acid differed by containing uracil instead of thymine. Carbohydrate and phosphorus were also known to be present. Virtually nothing, however, was known about its structure and function. The work of Levene allowed some conclusions to be drawn on these issues.
In 1909 Levene found that the carbohydrate present in yeast nucleic acid is the pentose sugar ribose; it was not, however, until 1929 that he succeeded in identifying the carbohydrate in thymus nucleic acid. It is also a pentose sugar but lacks one oxygen atom of ribose and was therefore called deoxyribose.
These facts enabled Levene to suggest a simple tetranucleotide structure for the inevitably named ribonucleic and deoxyribonucleic acids (RNA and DNA). (A nucleotide is simply one of the four bases plus a sugar and a phosphate group.) According to Levene each of the four bases occurred just once in each DNA and RNA molecule and were joined together by the sugar and phosphate groups. This structure could then be repeated to form a polynucleotide with the bases occurring in the same order throughout.
Levene had succeeded in establishing the nucleic acids as genuine molecules existing independently of the proteins but the price he paid for this clarification was to impose on them an absurdly simple and repetitive structure. Consequently, when the search for biological individuality reached the molecular level, the far more complex and varied structure of the proteins was favored over the ‘monotonous’ form of the nucleic acids, and a generation of biochemists mistakenly sought for the structure of the gene among the inexhaustible potential of the amino acids.
When Levene was told, shortly before his death, of the classic work of Oswald Avery, which showed the crucial part played by DNA, he was reported to be skeptical. It took a further 13 years before James Watson and Francis Crick came up with their famous double helical structure and completed the revolution begun by Levene and other biochemists earlier in the century.
