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J. Biol. Chem., Vol. 282, Issue 18, 13, May 4, 2007
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Classics
Oligonucleotides as Primers for Polynucleotide Phosphorylase
(Singer, M. F., Heppel, L. A., and Hilmoe, R. J. (1960) J. Biol. Chem. 235, 738–750)
The Polymerization of Guanosine Diphosphate by Polynucleotide Phosphorylase
(Singer, M. F., Hilmoe, R. J., and Heppel, L. A. (1960) J. Biol. Chem. 235, 751–757)
A Binding Protein for Glutamine and Its Relation to Active Transport in Escherichia coli
(Weiner, J. H., and Heppel, L. A. (1971) J. Biol. Chem. 246, 6933–6941)
Leon A. Heppel was born in Granger, Utah in 1912. Several years later, he and his family moved to San Francisco, where Heppel attended school and became interested in chemistry. While in high school, Heppel's mother got him a job doing analytical work at the American Cream Tartar Company. The job supported him through high school and afterward when he enrolled at the University of California, Berkeley as a chemistry and chemical engineering major. Unfortunately, American Cream Tartar's parent company, Stauffer Chemical Company, merged with the Schilling Spice Corporation in 1931, and, as Heppel recalls, "A vice president of Schilling Spice undertook to effect economies, but the only economy he could find was getting rid of me. Shocked and urged by my mother to plead my case, I told the vice president how much I depended on the job. His cold reply was, `You need Schilling Spice Company but does Schilling Spice need you?' I never forgot those cruel words. Because of them, I abandoned my plan to be a chemical engineer, turning instead to physiological biochemistry, which I thought would be a gentler profession" (1).
Fortunately, Heppel received a fellowship allowing him to complete his B.S. degree. He graduated in 1933 and entered Berkeley's graduate school as a biochemistry student. Heppel did his thesis with C. L. A. Schmidt, studying potassium metabolism in rats. He was awarded his Ph.D. in 1937 but had a lot of trouble finding a job. Luckily, Schmidt came to the rescue and got Heppel a partial fellowship to attend medical school at the University of Rochester. At Rochester, Heppel joined W. O. Fenn's laboratory, where he continued to work on potassium metabolism in young rats. He completed his M.D. and internship in 1942. Then, the entry of the United States into World War II interrupted normal peacetime activities, and Heppel joined the United States Public Health Service. He was assigned to the National Institutes of Health (NIH) where he carried out studies on the toxicity of halogenated hydrocarbons.
After the war, Heppel remained at the NIH and joined the new research section for the study of enzymes. He eventually became the chief of the Laboratory of Biochemistry and Metabolism at the National Institute of Arthritis and Metabolic Diseases. After establishing his lab at the NIH, Heppel turned his attention to the phosphorylation and hydrolysis of purine ribonucleosides, which led to an interest in enzymes that hydrolyze RNA. By 1950, Heppel and his technician Russell J. Hilmoe had begun to do experiments on enzymes that catalyze the hydrolysis and phosphorolysis of polyribonucleotides and their derivatives. They studied 5'-nucleotidase, inorganic pyrophosphatase, and the hydrolysis and phosphorolysis of purine ribosides and ATP. Then, in 1955, Severo Ochoa and Marianne Grunberg-Manago discovered polynucleotide phosphorylase (PNPase), an enzyme that converted ADP and other nucleoside diphosphates into RNA-like (NMP)n polymers. This was the subject of a previous Journal of Biological Chemistry (JBC) Classic (2). Ochoa and Grunberg-Manago turned to Heppel for help in characterizing the polymer products produced by PNPase.
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In the first Classic, Singer, Hilmoe, and Heppel show that short oligonucleotides can serve as primers for PNPase. Specifically, they found that oligoribonucleotides with an unesterified, terminal, C-3' hydroxyl group served as primers for the polymerization of adenosine 5'-diphosphate, uridine 5'-diphosphate, and thymine ribonucleoside pyrophosphate catalyzed by polynucleotide phosphorylase. The oligonucleotides were starting points for chain proliferation but were not incorporated into the finished polymer.
In the second Classic, the researchers discuss the polymerization of guanosine diphosphate by PNPase. They showed that GDP, when present alone, is not polymerized by enzyme fractions from Agrobacterium agile or Escherichia coli. However, polymerization of GDP did take place in the presence of oligonucleotide primers with an unsubstituted hydroxyl group at carbon 3' of the terminal nucleoside residue. Unlike polymerization reactions with adenosine 5'-diphosphate, uridine 5'diphosphate, and thymine ribonucleoside pyrophosphate, the primers were incorporated into the polymer.
These experiments showed how mixed polyribonucleotides of various kinds could be synthesized. Some time later, Singer and Heppel used PNPase to prepare the polyribonucleotides and oligoribonucleotides that Marshall Nirenberg and Heinrich Matthei used in their experiment that defined the genetic code for phenylalanine.
In 1967, Heppel left the NIH to become a professor of biochemistry at Cornell University, where he remains today as a Professor Emeritus. By the time he moved to Cornell, Heppel's research focus had shifted to the properties of bacterial membranes. His work on sugar- and amino acid-binding proteins found in the periplasmic space of E. coli and other bacteria is the subject of the last JBC Classic reprinted here. Along with his graduate student Joel Weiner, Heppel investigated glutamine uptake in E. coli and showed that the bacteria contains a specific binding protein for glutamine, which they isolated, purified, and characterized. Their data suggested that this protein played a role in the active transport of the amino acid across the bacterial membrane. Subsequent work by Heppel and others defined a large class of binding protein-dependent transport systems in bacteria.
Heppel was also instrumental in Earl Sutherland's identification of cAMP. As explained in a previous JBC Classic (3), Sutherland and Ted Rall had discovered that increased formation of phosphorylase in the liver was mediated by a heat-stable factor. Sutherland wrote to Leon Heppel hoping that he might be able to help elucidate the structure of this molecule. Around the same time, David Lipkin wrote Heppel describing a new nucleotide that was produced by treating ATP with barium hydroxide. Heppel deduced that Sutherland and Lipkin were studying the same molecule, which turned out to be adenosine 3',5'-monophosphate, now commonly referred to as cyclic AMP or cAMP.
Heppel has received many honors and awards in his career including the 1959 Hillebrand Prize of the Chemical Society of Washington. He is a member of both the National Academy of Sciences and the American Academy of Arts and Sciences.1
Heppel's co-author on the first two papers, Russell J. Hilmoe, played an important role in the history of the American Society for Biochemistry and Molecular Biology. In 1975 he succeeded Robert A. Harte as the second Executive Officer of the society and Manager of the JBC and served until 1979. Hilmoe earned his B.S. degree from South Dakota University and his Ph.D. in Biochemistry from Georgetown University. During World War II he served in the U.S. Army Medical Corps and then with the U.S. Army Chemical Corps. In 1948 he became an intramural scientist in the National Institute of Arthritis and Metabolic Diseases at the National Institutes of Health, and in 1964 he became a science administrator in the National Institute of General Medical Sciences and oversaw extramural research grant support and graduate biomedical research training.
FOOTNOTES
1 Biographical information on Leon A. Heppel was taken from Refs. 1 and 4. 
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