The Use of Cell-Free Systems in Studying Saccharide Assembly Some Problems

The Use of Cell-free Systems in Studying Saccharide Assembly Some Problems 

The point at which such a cell-free system can be considered to be functionally competent is somewhat arbitrary. Very few such systems can achieve rates of synthesis comparable with those found in the intact cell and they are commonly less efficient by one to two orders of magnitude. Anything much less than this would generally be considered as unacceptably inefficient, unless there was very good evidence for regarding it as a true model of physiological biosynthesis. 

These hazards are probably more serious in the study of saccharide assembly than in the synthesis of polypeptide. The absolute requirement for a message in the form of a linear polynucleotide, to specify the particular amino acyl transfers that can occur, largely prevents the possibility of inappropriate synthesis of polypeptide, and powerful techniques exist for identifying and characterising the labelled products of such synthesis. While the true rates of various steps in this process may be distorted in a cell-free system, the sequence of events and the mechanisms of each step are demonstrably almost unaltered and are accessible to detailed analysis. With oligo- and poly-saccharides there can be difficulties and these must be clearly appreciated in evaluating much of the work to be described below and in the chapters that follow. 

The problems outlined above seem formidable, but they are seldom insuperable, provided that they are recognised and appropriate precautions are taken and control experiments performed. 

---