Choh Hao Li (sometimes Cho Hao Li) (Chinese: 李卓皓; pinyin: Lǐ Zhuōhào; April 21, 1913 – November 28, 1987) was a Chinese-born American biochemist who discovered in 1966 that human pituitary growth hormone (somatotropin) consists of a chain of 256 amino acids. In 1970, he succeeded in synthesizing this hormone, the largest protein molecule synthesized up to that time.
Li was born in Guangzhou and educated at the Nanjing University. In 1935, he immigrated to the US, where he took up postgraduate studies at the University of California, Berkeley, and later joined the staff. He became professor in 1950. He served as Director of the Hormone Research Laboratory at Berkeley from 1950 to 1967 and at UCSF from 1967 until his retirement in 1983. In 1955, he was elected as Academician of Academia Sinica, Republic of China.
Li dedicated his entire academic career studying the pituitary-gland hormones. In collaboration with various co-workers, he isolated several protein hormones, including adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex to increase its secretion of corticoids. In 1956, Li and his group showed that ACTH consists of 39 amino acids arranged in a specific order, and that the whole chain of the natural hormone is not necessary for its action. He isolated another pituitary hormone called melanocyte-stimulating hormone (MSH) and found that not only does this hormone produce some effects similar to those produced by ACTH, but also that part of the amino acid chain of MSH is the same as that of ACTH.
In 1940, Li successfully purified the luteinizing hormone from sheep pituitary glands. The whole process included grinding thousands of glands, extracting the hormone, and then identifying its chemistry and biology at the molecular level. This was a breakthrough in biological studies.
Eight of the nine hormones secreted by the anterior pituitary were isolated and identified by Li and his research team. These nine hormones can be divided into three groups based on the similarity of their chemical properties and biological activities.
The first group includes adrenocorticotropic hormone (ACTH), melanocyte-stimulating hormones (MSH), and lipotropin.
1953 - Li was the first to isolate and extract ACTH.
1964 - Li and his research team discovered and isolated lipotropin, and its structure was defined in 1965.
1975 - Li discovered β-endorphin when trying to find β-lipotropin in camel brain. The team isolated human β-endorphin in 1976 and synthesized it to study its biological activity after they defined the structure of β-endorphin.
The second group includes follicle stimulating hormone (FSH), luteinizing hormone (LH), and thyroid stimulating hormone (TSH).
1974 - Li and his team sequenced human LH and TSH.
The third group includes growth hormone and prolactin.
1944 - Li was the first person to isolate growth hormone from cow brains. The lack of function of cow growth hormone on human body motivated Dr. Li to find human growth hormone.
1956 - Li successfully isolated human and monkey growth hormone and demonstrated its efficacy to treat hypopituitary children.
1969 - Li discovered the complete primary structure of sheep prolactin.
1970 - Li synthesized proteins with human growth hormone activity.
Li was an expert in diversified areas, including endocrinology, biochemistry, and peptide synthesis. He not only was a widely recognized leader in pituitary-secreted research for his contribution in hormone and growth factors, but also greatly advanced the field of protein chemistry. All of his research had direct impact on clinical applications, especially in growth and fertility. It is estimated that he had published more than 1,000 research papers and had collaborated with more than 300 people. In addition, he was also the recipient of a lot of honors (more than 25). The most significant ones are as follows:
1947 - the Ciba Award from the Endocrine Society