Multiple Scientific Paths in Boston

INTESTINAL ALKALINE PHOSPHATASEAs the Schmidts settled into life in Brookline, Gerhard dove into research at the Dispensary. His first project, on alkaline phosphatase, was a good match for his developing interests as well as those of Thannhauser, who had published five articles the previous year concerning the increase of this enzyme activity in the serum of patients with certain diseases, Gerhard was fascinated by several aspects of phosphatases: their diversity, specificities, optimal conditions, and application as tools for studying structures of phosphate-containing substances, especially nucleic acids and nucleotides, but now phospholipids as well. The broader question of the roles of phosphatases in metabolism also stimulated him. It was easy to see that they were involved in breakdown of phosphate-containing organic compounds, just as other hydrolytic enzymes were involved in breakdown of polysaccharides, proteins, and lipids. A more difficult issue was how these complex structures were synthesized in living cells. At that time, very little was known about biosynthetic processes. Some scientists explored the possibility that synthesis could simply be a reversal of hydrolysis. At the Rockefeller Institute, for example, Bergmann had shown a sort of peptide bond synthesis with papain;1 and in St. Louis Gerhard had shown reversibility of phosphorylase-catalyzed activity.2 It was soon learned, however, that biosynthesis generally follows a more complex pathway than just the reverse of hydrolysis, with formation of intermediate compounds that reflected energy-dependent activation of substrates.In view of Thannhauser's interests and his own, Gerhard began to study the alkaline phosphatase of intestinal mucosa. He set out to develop a largescale purification to produce enough enzyme of high enough purity to allow careful study of its catalytic properties, including its activation or inhibition by various substances. He at last gave up the gravimetric method for measuring inorganic phosphate, the product of enzyme catalysis, and adopted a colorimetric method, using either the procedure developed by Fiske and Subbarow at Harvard University, or that of Delory in England.3As a starting source of enzyme, he made a suspension of the mucosa scraped from 6 feet of calf intestine. He encountered a problem in trying to obtain soluble enzyme. The enzyme was bound firmly to cell walls, and it appeared in an insoluble lipid-rich layer lying over the water and watersoluble materials. He reflected that, according to the standards of the early 1940s, it was essential to prepare an enzyme in soluble form if one wanted to study it and hoped to publish a description of its properties. Looking back much later, he said, with a chuckle, "To submit a paper to an editor on an enzyme that had not been made soluble was about the same as to go on New Year's Eve to the Metropolitan Opera in a turtleneck sweater." Fortunately he found that, if he treated the suspension with trypsin, the phosphatase was released from cell surfaces; the enzyme, itself, was resistant to digestion by trypsin, so it became water soluble and retained its activity. With a 30% yield of total starting activity, he obtained a highly active, substantially purified enzyme.4These data were presented in the Journal of Biological Chemistry in 1943, in the first article Gerhard published from his new base in Boston.5 In addition to this work on intestinal phosphatase in his first years in Boston, he joined Thannhauser in writing a major review of research on the chemistry of lipins for the 1943 Annual Review of Biochemistry.6He then had to determine his long-term scientific directions. Thannhauser had made clear that he could work on any project of his own choosing. That freedom was an opportunity to pursue his longstanding interests in nucleic acids and nucleotides, materials that Thannhauser had studied extensively in Germany. On the other hand, he felt a responsibility to consider that Thannhauser's main efforts in Boston were on phospholipids, particularly focused on nervous system diseases and lipidoses (diseases of lipid metabolism), and that all of the funding for the laboratory was obtained by Thannhausen He therefore would put at least part of his effort into supporting that work. …