[1] He was professor at the Humboldt University of Berlin, and best known as one of the founders, with Tom Rapoport, of metabolic control theory[2] in parallel with similar ideas developed at about the same time by Henrik Kacser and Jim Burns.

Working with Tom Rapoport on mathematical models of glycolysis in red blood cells, Reinhart discovered a precise and general definition of rate limitation in metabolic pathways, for which he received in 1974 the Humboldt Prize.

Instead of postulating a single rate-limiting step, these theories evaluated the degree of flux control exerted by an individual enzyme in a linear pathway or in a more complex network.

[6] To understand the kinetic design of enzymes and enzymatic reaction networks, Reinhart strove to rationalize, in mathematical terms, the selective pressures and physico–chemical constraints that these systems were subjected to.

In addition to this large body of original work, he was a gifted mentor of young scientists and for more than ten years ran the highly successful interdisciplinary graduate program Dynamics and Evolution of Cellular Processes at Humboldt University, Berlin.