(August 2003) As early as the 19th century it was known that phosphates could be bound to proteins. Most examples of these ‘phosphoproteins’ were found in milk (caseins) and egg yolk (phosvitin) and were simply considered a biological method of providing phosphorus as a nutrient. Therefore, the existence of phosphoproteins was considered a consequence of metabolic reactions, and nothing more, for almost a century after their discovery [1]. In the 1950’s this all began to change as phosphoproteins began to emerge as key regulators of cellular life. An initiating factor of this emergence occurred in 1954, when an enzyme activity…