text: In a review of earlier work on catecholamine biosynthesis, German-British biochemist Hermann Blaschko (1900–1993) wrote: "Our modern knowledge of the biosynthetic pathway for the catecholamines begins in 1939, with the publication of a paper by Peter Holtz and his colleagues: they described the presence in the guinea-pig kidneys of an enzyme that they called dopa decarboxylase, because it catalyzed the formation of dopamine and carbon dioxide from the amino acid L-dopa." The paper by Peter Holtz (1902–1970) and his coworkers referred to in that quote originated from the Institute of Pharmacology in Rostock. Already in that same year, both Blaschko at Cambridge and Holtz in Rostock predicted the entire sequence tyrosine → l-DOPA → oxytyramine = dopamine → noradrenaline → adrenaline.  Edith Bülbring, who also had fled National Socialist racism in 1933, demonstrated methylation of noradrenaline to adrenaline in adrenal tissue in Oxford in 1949, and Julius Axelrod detected phenylethanolamine N-methyltransferase in Bethesda, Maryland in 1962. The two remaining enzymes, tyrosine hydroxylase and dopamine β-hydroxylase, were also characterized around 1960.
  Even before contributing to the formation pathway, Blaschko had discovered a destruction mechanism. An enzyme tyramine oxidase described in 1928 also oxidized dopamine, noradrenaline and adrenaline. It was later named monoamine oxidase. This seemed to clarify the fate of the catecholamines in the body, but in 1956 Blaschko suggested that, because the oxidation was slow, “other mechanisms of inactivation … will be found to play an important part. Here is a gap in our knowledge which remains to be filled.” Within a year, Axelrod narrowed the gap by showing that dopamine, noradrenaline and adrenaline were O-methylated by catechol-O-methyl transferase. To fill the gap completely, however, the role of membranes had to be appreciated ().