Catabolism of the Plasma Proteins

Abstract

Each plasma protein component has a special life span of its own. A part of the body pool is continuously being destroyed while the same quantity is being synthesized anew. This keeps plasma proteins in a state of dynamic equilibrium, thus making it possible to determine the degradation rate or the catabolic rate as described previously. Moreover, the degradation rate and the synthetic rate should be equal, if the plasma protein metabolism in the body of a patient is in a steady state during the period of its study. Therefore, the degradation rate of plasma proteins which are in a steady state is also called as the turnover rate, and the degraded quantity per day, as the turnover. The turnover rate is sometimes expressed as g/day, but because the turnover differs according to bodily weight, the turnover rate is expressed as g/kg/day, using one kilogram of body weight as a basis for calculation. However, under abnormal conditions where plasma protein catabolism varies, it is of course impossible to obtain the synthetic rate from the degradation rate. Accordingly, to obtain the synthetic rate, the method by Grossma et aí.⁵⁴⁾ who use ¹³¹I—labeled protein, or a complicated procedure of measuring biosynthesis directly should be employed.¹³³⁾