KUNITZ, MOSES

(b. Slonim Russia, 19 December 1887; d. Philadelphia, Pennsylvania 21 April 1978), Physical biochemistry, enzymology.

Kunitz was born in Slonim, in Russia. After World War I Slonim was reincorporated within the USSR, in the state of Belorussia. The town has been described as a center of Talmudic studies, before it was occupied by the German army in 1941. The changes in the fortunes of slonim and its Jewish community were undoubtedly a matter of concern to Kunitz throughout his life in the United States, and he participated in reunions in New York of emigrants from Slonim. Kunitz emigrated to the United States in 1909, obtained a job in a factory making straw hats, and entered the Cooper Union Evening School of Chemistry in New York in 1910. He then brought his brother and wife-to-be, Sonia Bloom, to America. He married in 1912; a daughter was born in 1914 and a son in 1921.

In 1913 he became the laboratory assistant of Jacques Loeb at the Rockefeller Institute, continuing in this position until 1923. He became a United States citizen in 1915. With Loeb’s encouragement Kunitz graduated from Cooper Union in1916 with a B.S. degree and continued his evening studies for two years at the Electrical Engineering School of Cooper Union and an additional year at the Extension School of Columbia University. Two more years were spent in the Columbia School of Mines, Engineering and Chemistry, and in 1922 Kunitz became a graduate student in biochemistry at Columbia University. Having worked day and night for almost a decade, he was appointed to the staff of the institute in 1923 with the title of assistant. In that year, Kunitz published two articles with Loeb on the effects of acids and salts on the behavior of proteins. His thesis at Columbia was a physiochemical study of the properties of gelatin in salt solutions, and he received a Ph.D. degree in 1924. He was a competent glassblower, and the first of his independent papers, published in 1924, ….published in 1924, salts on sodium salts of gelatin. Kunitz concluded the latter with an expression of indebtedness to Loeb. Loeb died in 1924 and Kunitz’s role and position in the institute then changed significantly.

Loeb’s interest in salt effects had grown markedly after his discovery of the artificial parthenogenesis of sea urchin eggs in seawater supplemented with Mg⁺⁺. The continuing analysis of the different effects of various cations and anions led to the detailed studies that Loeb carried out with the initially meticulous, later skilled and knowledgeable, Kunitz. These studies eventually demonstrated the weakness of theories of colloid chemistry in explaining the behavior of proteins, rejected some commonly held views, and asserted the importance of controlling hydrogen ion concentration (or pH) in determining the binding of ions by proteins. Kunitz’s definitive laboratory work in the last years of Loeb’s life established the former as a significant figure in studies of the physical chemistry of proteins.

When Loeb’s major colleague, John H. Northrop, in the department of general physiology, was appointed to head that division after Loeb’s death he invited Kunitz to stay and to continue these physiochemical studies. Northrop and Kunitz published many papers together on ion binding swelling osmotic pressure and other properties of gelatin, as well as on related topics, from 1924 to 1931. In 1926 Kunitz was promoted to an associateship at the institute at the recommendation of Northrop. He had demonstrated unusual and useful skills in mathematics, as well as in the experimental physical chemistry of proteins.

In 1926 Northrop, who preferred country life, transferred his group to the branch of the institute in Princeton, New Jersey, containing the departments of animal and plant pathology. Kunitz also moved with Northrop to the relatively new laboratories, organized by The obald Smith in 1916and 1917. It may be mentioned that some new members of this branch of the institute including “the physiologists” Northrop and Kunitz, were viewed by Smith as an administrative burden.

As early as 1919 Northrop had begun to work on proteolysis by pepsin, and he now concentrated on proteinases. Following the reported crystallization of urease by J. B. Sumner in 1926. Northrop advanced to the crystallization of pepsin by 1930. Kunitz then began work on the purification of pancreatic enzymes, and in 1931 the collaborators reported the crystallization of trypsin. The skills of Kunitz, honed on the physical chemistry of gelatin, were now brought to bear on enzyme isolation and characterization, and in the next three decades produced numerous landmarks in the development of enzymology. In the transition of the work of the laboratory, gelatin was used to detect the presence of proteolytic gelatinases and to assay such enzymes.

In 1930 Northrop was concerned with the problem of establishing the purity of crystals of pepsin. of determining whether such crystals contained one protein or a mixture of proteins of similar solubility. Application of the theory of the phase rule enabled him to demonstrate that the phase crystals contained a single protein. Determination of the solubility of pepsin protein. Determination of the solubility of should, and indeed did, give a single value for the solubility of the protein. In 1930 also, Northrop and Kunitz considered the general theory of solubility curves obtainable from mixtures or solid solutions of proteins. This now became a major approach to the establishment of the purity of the many proteins isolated by these investigators. Kunitz, in collaboration with M. L. Anson and Northrop, also developed methods of establishing the molecular weight, molecular volume, and hydration of various proteins. In 1932 the methodologies were applied to crystalline trypsin, and the range of activity of the enzyme and its molecular properties were described. Kunitz and Northrop studied the irreversible and reversible denaturation and inactivation of the enzyme in 1934. A classical study of the thermodynamics of the reversible denaturation of a trypsin inhibitor was published by Kunitz in 1948.

In 1933 Kunitz and Northrop extracted the proenzyme chymotrypsinogen from pancreas with cold sulfuric acid (o.12 M), crystallized the protein, and demonstrated its conversion by trypsin to the active proteolytic enzyme chymotrypsin, which was also proteolytic enzyme chmotrypsin, which was also crystallized. This discovery began to explain the long-known fact that fresh pancreas lacked active tisswue-digesting proteolytic enzymes. The following year they showed that trypsin is similarly contained in the acid extract as the crystallizable trypsinogen, itself activatable by trypsin. The generality and consequences of the paring of proproteins to functional proteins have become clear only after some thirty years. Many of the peptides removable by proteolysis or other active fragments of the degradation of proteins have more recently been found to possess striking physiological effects in themselves. The presence of leading hydrophobic sequences, subsequently removable, have been shown to be important in the secretion of proteins through membranes. Autodigestible giant proteins have been detected in the multiplication of an RNA virus, such as that of foot-and mouth disease. The arrest of proteolytic fragmentation is a possible approach to blocking the multiplication of such a virus, a problem of great interest to Theobald Smith.

By 1934 and 1935, as Northrop extended his work in other directions. Kunitz took the leadership in studies of the pancreatic proenzymes and on the activity and inhibition of the enzymes themselves. The startling success of Northrop and Kunitz in the institute in Princeton led their younger colleague, Wendell Stanley, in the nearby department of plant pathology, to exploit similar methods to isolate tobacco mosaic virus. This ambitious effort succeeded in 1935, and a group of young biochemists worked under Stanley’s leadership in Princeton until these laboratories were closed at the end of the 1940’s. In this period Kunitz was a warm and fatherly figure in assisting the younger people attracted by the laboratories of Northrop and of Stanley.

Prior to American involvement in World War II, Kunitz continued to explore the Kinetics of conversion of the zymogens to active enzyme. With Northrop he discovered and crystallized a pancreatic basic protein that combines with and inhibits the appearance of active trypsin. He also turned to the isolation of pancreatic nucleases. In 1939 and 1940, exploiting once again the extraordinary stability of some proteins in acid, he described the isolation and crystallization of a small, heat-stable ribonuclease, whose contamination by proteinase was subsequently eliminated by heat. The availability of this enzyme, as well as of crystalline deoxyribounclease, whose isolation he reported in 1948 became major tools in the subsequent exploration of the structure and function of the nucleic acids beginning in the 1940’s.The specific degradation and inactivation of genetic function by the purified nucleases became crucial elements of proof that pneumococcal DNA was an agent of inheritable transformation in 1944 or that viral RNA or DNA were infectious genetic units in the late 1950’s. Almost immediately Kunitz’s enzymes, eventually made available commercially, became essential tools in the progress of the biochemistry of the nucleic acids and in molecular biology. Ribonuclease itself became a protein of choice for the analysis of unfolding and inactivation and spontaneous refolding and regeneration of active enzyme. In 1940 Kunitz was promoted to associate membership in the Rockefeller Institute.

Early in the American involvement in World War II, Kunitz was asked by a civilian governmental agency, the Office of scientific Research and Development, to isolate hexokinase from yeast, as was the laboratory of carl Cori. Both groups succeeded, Kunitz publishing this work in 1846 with Margaret McDonald, with whom he had worked on several problems of protein isolation since 1940. Characteristically. in the course of his investigation of hexokinase, he first crystallized three other proteins, only one of which was readily defined as an enzyme. Kunitz and McDonald also crystallized the toxic ricin, which, according to R. Herriott, was recalcitrant to other workers. In later years Kunitz became the crystallizer of last resort for many younger enzyme chemists.

In 1946 Sumner, Northrop, and Stanley were awarded the Nobel Prize for their work in crystallizing proteins, and in 1948 a second edition of the book Crystalline Enzymes (first published in 1939), containing the elegant work of Northrop, Kunitz, and Herriott, appeared. The volume is, in fact, a manual summarizing and detailing their most important studies and marks the end of their close departmental association. In 1947 the board of trustees of the Rockefeller Institute decided to close the Princeton branch and to merge it with the larger branch in New York. In the next year a dozen members of the Princeton staff, including Northrop and Stanley, elected to leave the institute. The Nobelists moved to the University of California at Berkeley, and the Princeton laboratories were closed in 1950. Almost a decade late, in 1957. Northrop called upon Kunitz once again, in an effort to define the nature of mutations in mathematical terms and to clarify problems in the development of lysogenic bacteriophage.

With Northrop’s move to California and the disruption of a collaboration extending some thirtyfive years, kunitz returned to the institute in New York, with a promotion to full membership in 1949. After the death of his wife, he had marired a former Slonimer in 1939. The coulpe welcomed their return to New York, enjoying the social and cultural oppotunities of the City. Kunitz was particularly fond of opera and found amiable colleagues with whom to play chess.

Now in his early sixties, Kunitz turned to several new enzymes and biological materials. In the early 1950’s he isolated and characterized an inorganic pyrophosphatase from yeast; in his last paper in 1962 he confirmed the observation that the enzyme also hydrolyzed adenosine triphosphate in the presence of Zn⁺⁺. In his last working years he had studied two extremely recalcitrant enzymes, the al kaline phosphatase of chicken intestine and an invertase of yeast. Despite his experience and artistry in coaxing protein crystals from solution, both enzymes possess unusual structural features and neither responded felicitously to his touch. It is not clear how Kunitz regarded his lack of success in obtaining pure crystalline products in these challenging final efforts. In 1953 Kunitz had become member emeritus at the institute. and in 1970 he was retired from the Rockefeller University, which awarded him an honorary degree in 1973.

Kunitz did not write reviews that integrated his studies into the developing thought of the time. With few exceptions. his papers do not tell us his thoughts on why enzymes. such as ribonuclease or inorganic pyrophosphatas, warranted his attention. To anyone discussing science with him at the Rockefeller Institute, it was clear that he was not attempting to keep up with the explosive advances of the biochemistry of the time; having devided on a project, he would sift the literature for essential information but would give his time, labor, and thought to the project at hand. He was delighted with the crystals as they appeared. but his deliberate efforts were marked, as Northrop has said, with’ imagination,ingenuity, persistence, great technical skill, mathematical facility. and a thorough theoretical knowledge.’ It is regrettable that in his long career he had so few students, as either postdoctoral fellows or technicians. Nevertheless. the many young fellows abounding at the Rockefeller Institute who were sufficiently courageous to peek into the laboratory of this living legend were given every opportunity to ask questions, to see Kunitz at work. and to learn a method under his friendly surveillance.

Kunitz was extremely modest and self-effacing. In 1957 he was awarded the Carl Neuberg Medal by the American Society of European Chemists and Pharmacists and in 1967 he was belatedly elected to the National academy of Sciences. He spent many summers working with Loeb and later with Northrop at the Marine Biological Laboratory in Woods Hole. Massachusetts. He enjoyed gardening at his summer home at Falmouth Heights in Massachusetts, now occupied by his son, Jacques Kunitz. Kunitz died in Philadelphia in the care of his daughter. Rosaline Albert.

BIBLIOGRAPHY

I. Original Works. A complete list of Kunitz’s publications is obtainable from the archives of the Rockefeller University. See also Poggendorff. Key publications to which references are made in the article include “Valency Rule and Alleged Hofmeister Series in the Colloidal Behavior of Proteins, I, The Action of Acids,” and “II The Influence of Salts,” in Journal of General Physiology, 5 (1923), 665–691 and 693–707, written with J. Loeb, and “III, The Influence of Salts on Osmotic Pressure, Membrane Potentials, and Swelling of Sodium Gelatinate,” ibid., 6 (1924), 547–564; “The Combination of Salts and Proteins, I,” ibid., 7 (1924), 25–38, written with J. H. Northrop; “Solubility Curves of Mixtures and Solid Solutions,” ibid., 13 (1932), 781–791, written with J. H. Northrop; “Crystalline Trypsin, I, Isolation and Tests of Purity,” ibid., 16 (1932), 267–294, written with J. H. Northrop; and “Molecular Weight, Molecular Volume, and Hydration of Proteins in Solution,” ibid., 17 (1934) 365–373, written with M. L. Anson and J. H. Northrop.

“Crystalline Chymo-trypsin and Chymo-trypsinogen, I. Isolation, Crystallization, and General Properties of a New Proteolytic Enzyme and Its Precursor,” ibid., 18 (1935), 433–458.written with J. H. Northrop; “Isolation from Beef Pancreas of Crystalline Trypsinogen, Trypsin, a Trypsin Inhibitor, and an Inhibitor-trypsin Compound,” ibid., 19 (1936), 991–1007, written with J. H. Northrop: “Crystalline Ribonuclease,” ibid., 24 (1940), 15–32: “Crystalline Hexokinase (Heterophosphatese [sic] Method of Isolation and Properties,” ibid., 29 (1946), 393–412, written with Margaret R. McDonald; Crystalline Enzymes, 2nd ed.(New York, 1948), written with J. H. Northrop and R. M. Herriott; “Isolation of Crystalline Desoxyribonuclease [sic]) from Beef pancreas,” in Science, 108 (1948), 19; “The Kinetics and Thermodynamics of Reversible Denaturation of Crystalline Soybean Trypsin Inhibitor,” in Journal of Physiology, 32 (1948), 241–269; “Crystalline Inorganic Pyrophosphatase Isolated from Baker’s Yeast,” ibid., 35 (1952), 423–450; and “Hydrolysis of Adenosine Triphosphate by Crystalline Yeast Pyrophosphatase. Effect of Zinc and Magnesium Ions.” ibid., 45 (1962), 31–46.

II. Secondary Literature. George W. Corner, A History of the Rockefeller Institute, 1901–1953: Origins and Growth (New York, 1965); Joseph S. Fruton, Molecules and Life (New York, 1972); and R. Herriott, “A Biographical Sketch of John Howard Northrop,” in Journal of General Physiology, 45 (1962), 1–16, and “Moses Kunitz,” in Nature, 275 (1978), 351–352.

Seymour S. Cohen