Alexander Dounce

Alexander Latham Dounce (December 7, 1909 – April 24, 1997) was an American professor of biochemistry. Among his fields of study were the isolation and purification of cellular organelles, protein crystallization, enzymes (specifically catalase), DNA binding proteins, and the chemical basis of protein synthesis. He also invented the Dounce homogenizer, which was named after him.

Biography

Alexander Dounce was born on December 7, 1909, in New York. He began his undergraduate studies at Hamilton College but later moved to Cornell University, where he also did his doctoral studies in the lab of James B. Sumner, a pioneer in protein crystallization. Dounce received his PhD in organic chemistry in 1935, the title of his thesis being "Study of dihydrofurans and the dehydration rearrangement of 2,3-ethylenic 1,4-diols". According to Marshall W. Nirenberg, another biochemist who knew Dounce personally, "during his [Dounce's] final doctoral exam when his doctoral committee got together to ask him questions after he had finished his thesis research, his mentor, Sumner, asked him the question, 'How do proteins synthesize other proteins?' He [Dounce] said that question remained in his mind ever since then." After the end of World War II, he focussed on studying cell nuclei and particularly the isolation of intact nuclei from tissue, which was a new field of research at the time. In 1952, Alexander Dounce and Ernest Kay, who was Dounce's first PhD student, published a new method for DNA isolation and purification from nuclei employing sodium dodecyl sulfate that became widely used. This order of synthesis, which has later been termed the "central dogma of molecular biology" by Francis Crick, is textbook knowledge today. However, it was not until 1958, when Crick coined the term central dogma and described the concept in more detail, that it gained widespread acceptance.

In the same review article, Dounce was also one of the first scientists to propose a genetic code in which nucleotide triplets code for each of the 20 proteinogenic amino acids. He correctly assumed that genes consist of nucleic acid sequences which determine the amino acid sequences of proteins, and that a protein's sequence determines its function. Based on these assumptions, Dounce speculated that, during protein synthesis, each amino acid would pair with an individual nucleotide; the two other nucleotides surrounding it would determine the specificity of the binding. While the actual mechanism turned out to be different, Dounce's hypothesis that nucleotide triplets code for amino acids was correct, and his speculations "helped lead to the deciphering of the code." A Dounce homogenizer or "Douncer" is a glass mortar and pestle with a very small clearance between the mortar and the pestle – in Dounce's original design as little as 0.0005 inches or about 13 micrometers. This allows for tissue and cells to be lysed by shear stress while leaving the smaller organelles intact. Dounce homogenizers are still commonly used today to isolate cellular organelles.

When Dounce's former mentor, James B. Sumner, died in 1955, Dounce wrote Sumner's obituary in Nature.

For the remainder of his career, Dounce continued his research on nuclei and their contents, catalase, and protein crystallization.

Dounce died on April 24, 1997, in Rochester, New York. He was survived by his wife, Anna Elizabeth Dounce, who was the daughter of botanist Donald Reddick, and by their three children Helen, Eric, and George.

Scientific publications

Key publications

Dounce's PhD thesis Description of the first crystallization of catalase An often-cited method for DNA isolation and purification Dounce's speculative review on the mechanism of protein and nucleic acid synthesis First detailed description of the Dounce homogenizers

Further publications

Complete list of PubMed-listed articles by Dounce