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C. K. Kung coauthored the 1977 purification of human erythropoietin with T. Miyake and E. Goldwasser. The preparation was tested by gel electrophoresis under several chemical conditions as well as by biological activity.^[ref]

The study illustrates complementary evidence in protein purification: activity establishes that a fraction retains the sought biological effect, while separation methods examine its composition. A single band is useful evidence of apparent purity, but it does not by itself identify the mechanism of a hormone's action.

E. Goldwasser investigated erythropoietin, the hormone supporting red blood cell production. A 1977 study with T. Miyake and C. K. Kung purified human erythropoietin from urine through seven separation steps.^[ref]

The work coupled protein purification to biological activity measurements. Following activity is essential when the desired protein is initially a tiny part of a complex sample: the largest protein peak need not contain the active hormone. The resulting preparation enabled experiments on an identified active material rather than an unexplained effect of crude urine.

Erythropoietin is a glycoprotein hormone that supports production of red blood cells, or erythropoiesis. It acts through the erythropoietin receptor on responsive precursor cells; the signal is not itself an oxygen-carrying substitute for hemoglobin. Experiments showed association of the receptor with JAK2 and activation of that protein kinase after erythropoietin stimulation.^[ref]

Purifying the hormone made its activity experimentally tractable. In 1977, researchers used seven separation steps on human urine, including ion-exchange chromatography and gel filtration, and reported $930$-fold purification with $21\%$ activity yield. The preparation had $70400$ activity units per milligram of protein.^[ref]

These quantities answer different questions. Specific activity asks how much biological effect remains per unit protein mass; yield asks how much starting activity survives purification. A preparation can become much purer while losing most of the original material.

T. Miyake led the byline of a 1977 report, with C. K. Kung and E. Goldwasser, describing purification of human erythropoietin. Ion-exchange chromatography, gel filtration and other separations yielded an active hormone preparation with $930$-fold purification and $21\%$ activity recovery.^[ref]

Purity and recovery measure different achievements. For a hypothetical starting sample with $100$ activity units, $21\%$ recovery leaves $21$ units even if most unwanted proteins have been removed. A high purification factor therefore does not mean that nearly all of the starting erythropoietin survived.