Willey Glover Denis (February 26, 1879 – January 9, 1929) was an American biochemist and physiologist.
 She was noted particularly for her collaborations with Otto Folin, including studies of protein metabolism.
 She was a pioneer in the field of clinical chemistry and the measurement of protein in biological fluids (blood, urine and cerebrospinal fluid.
 She also developed the first reliable method of assaying lead in body tissue and waste.
Frederic Middlebrook Richards (August 19, 1925 – January 11, 2009), commonly referred to as Fred Richards, was an American biochemist and biophysicist known for solving the pioneering crystal structure of the ribonuclease S enzyme in 1967 and for defining the concept of solvent-accessible surface.
 He contributed many key experimental and theoretical results and developed new methods, garnering over 20,000 journal citations in several quite distinct research areas.
 In addition to the protein crystallography and biochemistry of ribonuclease S, these included solvent accessibility and internal packing of proteins, the first side-chain rotamer library, high-pressure crystallography, new types of chemical tags such as biotin/avidin, the nuclear magnetic resonance (NMR) chemical shift index, and structural and biophysical characterization of the effects of mutations.
Phoebus Aaron Theodore Levene, M.D. (25 February 1869 – 6 September 1940) was an American biochemist who studied the structure and function of nucleic acids.
 He characterized the different forms of nucleic acid, DNA from RNA, and found that DNA contained adenine, guanine, thymine, cytosine, deoxyribose, and a phosphate group.
Protein phosphorylation is a post-translational modification of proteins in which an amino acid residue is phosphorylated by a protein kinase by the addition of a covalently bound phosphate group.
 Phosphorylation alters the structural conformation of a protein, causing it to become activated, deactivated, or modifying its function.
 The reverse reaction of phosphorylation is called dephosphorylation, and is catalyzed by protein phosphatases. Protein kinases and phosphatases work independently and in a balance to regulate the function of proteins.
 The amino acids most commonly phosphorylated are serine, threonine, and tyrosine in eukaryotes, and histidine in prokaryotes, which play important and well-characterized roles in signaling pathways and metabolism.
 However, many other amino acids can also be phosphorylated, including arginine, lysine, and cysteine.
 Protein phosphorylation was first reported in 1906 by Phoebus Levene at the Rockefeller Institute for Medical Research with the discovery of phosphorylated vitellin.
 However, it was nearly 50 years until the enzymatic phosphorylation of proteins by protein kinases was discovered.
Edmond Henri Fischer (born April 6, 1920) is a Swiss American biochemist.
 He and his collaborator Edwin G. Krebs were awarded the Nobel Prize in Physiology or Medicine in 1992 for describing how reversible phosphorylation works as a switch to activate proteins and regulate various cellular processes.
 From 2007 until 2014, he was the Honorary President of the World Cultural Council.
Robert William Holley (January 28, 1922 – February 11, 1993) was an American biochemist.
 He shared the Nobel Prize in Physiology or Medicine in 1968 (with Har Gobind Khorana and Marshall Warren Nirenberg) for describing the structure of alanine transfer RNA, linking DNA and protein synthesis.
Albert Lester Lehninger (February 17, 1917 – March 4, 1986) was an American biochemist in the field of bioenergetics.
 He made fundamental contributions to the current understanding of metabolism at a molecular level.
 In 1948, he discovered, with Eugene P. Kennedy, that mitochondria are the site of oxidative phosphorylation in eukaryotes, which ushered in the modern study of energy transduction.
 He is the author of a number of classic texts, including: "Biochemistry, The Mitochondrion, Bioenergetics " and, most notably, his series "Principles of Biochemistry".
 The latter is a widely used text for introductory biochemistry courses at the college and university levels.
Roger Yonchien Tsien (; February 1, 1952 – August 24, 2016) was an American biochemist.
 He was a professor of chemistry and biochemistry at the University of California, San Diego and was awarded the 2008 Nobel Prize in Chemistry for his discovery and development of the green fluorescent protein, in collaboration with organic chemist Osamu Shimomura and neurobiologist Martin Chalfie.
 Tsien was also a pioneer of calcium imaging.
Susan Taylor (born 1942) is an American biochemist who is a Professor of Chemistry and Biochemistry and a Professor of Pharmacology at the University of California, San Diego.
 She is known for her research on protein kinases, particularly protein kinase A.
 She was elected to the Institute of Medicine and the United States National Academy of Sciences in 1996.
Dario Alessi FRSE FRS (born in France, 1967) is a biochemist, Director of the Medical Research Council Protein Phosphorylation and Ubiquitylation Unit (MRC PPU) and Professor of Signal Transduction, at University of Dundee.

Question: What American biochemist, born February 1869 was first responsible for reporting Protein phosphorylation? 
Answer: Phoebus Levene