ABSTRACT
Plasma proteins are a periodical source of perplexity to every long-term investigator because of the problems involved in the elucidation of their number, functions, structures, metabolism, evolution, and genetic variations; moreover, formidable difficulties often present themselves with the isolation and purification of plasma proteins, and invariably by attempts at their classification. The concept of plasma protein turnover entails the metabolic replacement of a quantity of protein by an equal amount of the same protein as the result of synthesis from precursors. Mass-spectrometric determination of stable isotope excesses in biological specimens was neither a fast nor an easy way of gathering metabolic information. The advent of radioisotopes in the second half of the 1940s is therefore to be viewed as a major technical advance. The composition of plasma with regard to proteins and other constituents is then summarily determined, and maintained within a broad range, by the metabolic activities and requirements of the individual organs.
