Proinsulin C-peptide (C-peptide) has drawn much research attention. Even if the peptide has turned out not to be important in the treatment of diabetes, every phase of C-peptide research has changed our view on insulin and peptide hormone biology. The first phase revealed that peptide hormones can be subject to processing, and that their pro-forms may involve regulatory stages. The second phase revealed the possibility that one prohormone could harbor more than one activity, and that the additional activities should be taken into account in the development of hormone-based therapies. In the third phase, a combined view of the evolutionary patterns in hormone biology allowed an assessment of C-peptide´s role in physiology, and of how biological activities and physiological functions are shaped by evolutionary processes. In addition to this distinction, C-peptide research has produced further advances. For example, C-peptide fragments are successfully administered in immunotherapy of type I diabetes, and plasma C-peptide levels remain a standard for measurement of beta cell activity in patients. Even if the concept of C-peptide as a hormone is presently not supported, some of its bioactivities continue to influence our understanding of evolutionary changes of also other peptides.

胰岛素原C肽（C肽）引起了很多研究关注。即使该肽在糖尿病治疗中不重要，但C肽研究的每个阶段都改变了我们对胰岛素和肽激素生物学的看法。第一阶段表明，肽激素可以进行加工，其形式可能涉及调节阶段。第二阶段揭示了一种激素可能具有不止一种活动的可能性，在开发基于激素的疗法时应考虑其他活动。在第三阶段，对激素生物学进化模式的综合看法允许评估C肽在生理学中的作用以及进化过程如何塑造生物活性和生理功能。除此区别外，C肽研究还取得了进一步的进展。例如，在I型糖尿病的免疫治疗中成功施用了C肽片段，血浆C肽水平仍然是衡量患者β细胞活性的标准。即使目前尚不支持C肽作为激素的概念，但其某些生物活性仍继续影响我们对其他肽的进化变化的理解。