RITTHAUSEN, KARL HEINRICH

(b. Armenruh bei Goldberg, Silesia [now Poland], 13 January 1826; d. Berlin, Germany, 16 October 1912)

agricultural chemistry, biochemistry.

Little appears to be known of Ritthausen’s parents and other relatives, or of his early life. After studying chemistry at Leipzig and Bonn, he began his chemical research in Liebig’s institute at Giessen, and was inspired by Liebig to follow a career in agricultural chemistry. Like Liebig, Ritthausen was concerned both with the advancement of basic chemistry and with the improvement of human and animal nutrition. He made his major contributions in a long series of studies on plant proteins, in the course of which he isolated two amino acids of major importance as products of protein hydrolysis, and developed methods of purifying, and in some cases crystallizing, plant seed proteins.

After working in Liebig’s laboratory, Ritthausen became assistant to Otto L. Erdmann at Leipzig (1852–1853), where he received the doctorate in 1853. From 1854 to 1856 he was director of the scientific department of the agricultural experiment station at Möckern, near Leipzig, then briefly director of the station at Ida-Marienhütte near Saarau in Silesia, not far from Breslau (now Wroclaw, Poland). In 1857 Ritthausen became professor of chemistry and physics at the Royal Agricultural Academy at Waldau, near Königsberg; in 1867 he went to Bonn as professor of chemistry at the agricultural college and director of its experiment station at Poppelsdorf. Here he married; the Ritthausens had a son and a daughter. In 1873 he became professor at the University of Königsberg (now Kaliningrad, U.S.S.R.), where he continued his work until his retirement in 1899. He was considered an outstanding teacher and a stimulating guide to his numerous research students. He moved to Berlin in 1903.

After an early period when he attempted a direct application of current chemical knowledge to the feeding of cattle, Ritthausen realized the need for further basic chemical studies and turned his attention to the study of plant proteins. In 1862 he began his studies on the proteins of wheat, which continued steadily over the next five years and led him into similar extensive work on proteins of legumes and of various oilseed proteins.

This work led to Ritthausen’s discovery of two dicarboxylic amino acids in protein hydrolysates, both present in amounts large enough to represent a substantial fraction of the whole protein. With the techniques then available, separation of a pure amino acid from the complex mixture represented by a hydrolyzed protein was no easy undertaking. Of more than twenty amino acids now known as regular constituents of proteins, only four—leucine, glycine, tyrosine, and serine—had been identified by 1865 as products of protein hydrolysis. Ritthausen was to add two more to the list. In 1866, working with proteins of wheat gluten that were soluble in alcohol-water mixtures (proteins later known collectively as gliadin), he obtained, after hydrolysis with sulfuric acid, excellent crystals of the previously unknown glutamic acid HOOC(CH₂)₂CH(NH₂)-COOH(α-aminoglutaric acid, C₅H₉NO₄). His own work, and that of others, soon demonstrated the presence of this amino acid in large quantities in hydrolysates of many other proteins.¹

Two years later Ritthausen was the first to isolate the closely related amino acid aspartic acid, HOOC CH₂ CH(NH₂)COOH-C₄ H₇ NO₄ from hydrolysates of proteins from lupines and from almonds. Unlike glutamic acid, aspartic acid was already well known. Its monoamide, asparagine, had been crystallized from asparagus juice by Nicolas Vauquelin and Pierre-Jean Robiquet in 1806. In 1827 A. Plisson had obtained crystalline aspartic acid by hydrolysis of asparagine, although controversy over the exact structure of these compounds continued for years. Ritthausen, however, was the first to demonstrate its presence in proteins.² He found that aspartic acid, like glutamic acid, was present in significant amounts in practically all proteins that he studied. In fact these two amino acids (or, as was realized later by Emil Fischer, their residues after elimination of water to incorporate them into peptide linkages) are almost entirely responsible for the acidic properties of proteins; thus Ritthausen’s discovery represented an important step forward.

In 1872 he published a book reviewing his work of the previous decade on the proteins of cereals, legumes, and oilseed plants. To extract these proteins from powdered and defatted seed meal, he commonly used mildly alkaline solutions of dilute potassium hydroxide as solvents. He also made much use of ethyl alcohol-water mixtures (commonly around 70 percent alcohol by volume) for extraction of the class of proteins later known as prolamins from the seeds of wheat, corn, and other plants. His use of alkaline solutions, however, came under severe criticism from Felix Hoppe-Seyler and his student T. Weyl.³ on the ground that the alkalinity of the extraction medium had irreversibly altered the character of the native protein.

Hoppe-Seyler and Weyl, like P. S. Denis and other earlier workers, preferred to use solutions of neutral salts as media for extracting proteins, and were concerned that acid and alkaline solutions would alter the proteins, perhaps irreversibly. Ritthausen considered their criticism unfair and published a detailed rebuttal. Their criticism, however, stimulated him to important studies on the use of neutral salts for extraction of plant seed proteins. He demonstrated that most of the proteins prepared by his earlier methods were still soluble in neutral salt solutions and unaltered in elementary composition. Among the proteins that he carefully described were several that could be readily obtained as well-formed crystals. In 1881 he described the preparation of a crystalline protein from hempseed, later named edestin and extensively studied by Thomas B. Osborne and others. Osborne, in his obituary of Ritthausen, noted that Ritthausen’s work had been unjustly neglected after about 1880, as a result of the criticisms of Hoppe-Seyler and Weyl.

Ritthausen’s work was not, however, confined to proteins. He studied many other constituents of seeds, obtaining vicin and convicin from vetch seeds, and he discovered in cottonseed the trisaccharide melitose, now known as raffinose.

Ritthausen began his work with the extremely simple concepts of protein chemistry that were current about 1850. In his long career he made substantial advances in recognizing that proteins from different sources were individually different to a far greater extent than had been realized earlier. His discovery of aspartic and glutamic acids in proteins was a major advance in a very difficult field. Other workers of a later generation, notably Osborne, director of the Connecticut Agricultural Experiment Station in New Haven, carried the study of plant proteins well beyond what Ritthausen had achieved. The techniques available to Ritthausen had achieved. The techniques available to Ritthausen were very limited, compared with those of later workers, but he did more than anyone else, in the generation after Liebig, to advance to chemistry of plant proteins.

NOTES

1. An excellent description of the chemical details of the work is given by Hubert B. Vickery and Carl L. A. Schmidt in “The History of Discovery of the Amino Acids”, in Chemical Riviews, 9 (1931), 169–318; see 221-224 for glutamic acid.

2. The history of aspartic acid and asparagine, with a detailed discussion of Ritthausen’s achievement, is given by Vickery and Schmidt (note 1), 198–207

3. Hoppe-Seyler’s criticism of Ritthausen was contained in his Physiologische Chemie, Pt. 1, Allgemeine Biologie (Berlin, 1877), 75f. The critique by Weyl, “Beiträge zur Kenntniss thierischer und pfanzlicher Eiweisskörper,” is in Hoppe-Seyler’s Zeitschrift für physiologische Chemic, 1 (1877–1878), 72–100; see esp, 84ff.

BIBLIOGRAPHY

I. Original Works. Ritthausen published one book, Die Eiweisskörper der Getreidearten, Hülsenfrüchte und Ölsamen: Beiträge zur Physiologie der Samen der Kulturgewächese, der Nahrungs-und Futtermittel (Bonn, 1872). This gives a good survey of his earlier work, with some historical background, but for details of his major contributions one must consult his papers.

Most of Ritthausen’s major work appeared in Journal für praktische Chemie from 53 (1851) to n.s. 30 (1884), with four papers in n.s. 59 (1899). For his initial discovery of glutamic acid in proteins, see “Über die Glutaminsäure,” in Journal für praktische Chemie, 42 (1866), 454–462. His first reprot on asperatic acid is “Über die zersetzungs-Produkte des Legumins und des Proteinkörpers der Lupinen und Mandeln beim Kochen mit Schwefelsäure,” ibid., 103 (1868), 233–238. A further report on both these amino acids is in ibid,, 107 (1869), 218–240. Among his numerous later papers of protein preparation and crystallization, two of a series from the Königsberg laboratory may be cited: “Zusammensetzung der Eiweisskörper der Hanfsamen und des kristallisierten Eiweisses aus Hanfund Ricinussamen,” ibid., n.s. 25 (1882), 130–137; and aus Kürbissamen,” ibid., 137–141. He published several papers 1877–1880) in Pflügers Archiv für die gesamte Physiologie, notably “Die Eiweisskörper der Pflanzensamen,” 15 (1877), 269–288, in which he replies in detail to the cirticisms of Hoppe-Seyler and Weyl. Studies on protins form various oilseeds are in ibid., 21 (1880), 81–104. He reported on vicin from Vicia sativa in “Ueber Vicin. Bestandtheir der Samen von Vicia sativa,” in Berichte der Deutschen chemischen Gesellschaft, 9 (1876), 301–304, Papers on vicin and alloxatin are in ibid., 29 (1896); “Wassergelt und Reaktion des Alloxantins,” 892–893; “Ueber Allozantin als Spaltungsprodukt des Convicins aus Saubohnen (Vicia faba minor) und Wicken (Vicia sativa),” 894–896; and “Vivin ein Glycosid,” 2108–2109.

II. Secondary Literature. The best account of Ritthausen’s life and work is Thomas B. Osborne, “Heinrich Ritthausen,” in Biochemical Bulletin (Columbia University Biochemical Association), 2 (1913), 335–339, with portrait and a comprehensive bibliography by L.W. Fetzer, 339–346. There is a brief notice, signed Stutzer, also with a portrait, in Berichte der Deutschen chemische Gesellschaft, 47 (1914), 591–593. See also Thomas B. Osborne, The Vegetable Proteins, 2nd ed., rev. (New York and London, 1924).

John T. Edsall