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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.

By T. Miyake, C. K. Kung and E. Goldwasser. Journal of Biological Chemistry 252(15), 5558–5564 (10 August 1977).

Abstract: seven-step purification from urine of patients with aplastic anemia; specific activity70400 units/mg,21%yield,930-fold purification; electrophoretic analyses.

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.