A mathematical model for the analysis of the turnover of protein mixtures. III. Practical problems in the investigation of heterogeneous protein pools.

In part 1 of this series [1] a model was presented fo the turnover of a protein pool consisting of proteins with different turnover constants which can be described mathematically by a set of integro-differential equations. As in the general case this system is not treatable analytically, a computer programme was developed to solve it numerically. The applicability of the programme and, more generally, of the model was tested using computer generated and real data. The analytical solutions of special cases (tracer elimination after pulse labeling and continuous labelling) which form modified power functions were given in part 2 [2]. on the basis of these functions problems of the design of experiments for a quantitative analysis of pool heterogeneities are discussed. In both cases a duration of the experiment of at least two or three times the reciprocal mean turnover constant turns out to be necessary; a combination of the two procedures is more appropriate. On the other hand, it is shown that after continuous labelling heterogeneity can largely be neglected. But with the experimental design f pulse labelling which is often used heterogeneity must always be taken into account even if it is not the direct object of the investigation since otherwise the calculated turnover constant is an error (too high by factor of about 2).