Techniques for the Measurement of Enzyme Degradation

Steady-State Methods for the Determination of Degradation Rate Constants 

Degradation rate constants may be determined under steady-state conditions either by following the conversion of a labeled precursor into the enzyme or by measuring loss of label from the enzyme pool after a brief pulse and effective dose. For both methods, it is essential that the enzyme can be isolated in a pure form from the tissue concerned. This is most conveniently accomplished by addition to the tis- 

The most convenient method of measuring the conversion of precursor to enzyme is by the constant infusion of radioactive amino acid. So long as enzyme is isolated at a time after the specific radioactivity of precursor has attained a constant value, multiple sampling of tissue is not needed. The fractional rate of enzyme synthesis (fc s), given in units of percent per day, can be obtained from a solution of the equation 

A measurement of the specific activity of the infused amino acid in the enzyme being studied is not immediately applicable to an antibody-enzyme precipitate because most of the protein in the precipitate is derived from the antibody rather than from the enzyme. However, 

Selection of an amino acid or precursor that mixes rapidly with a large body pool. Examples suitable for liver are guanidino-labeled arginine, since this is rapidly converted to urea and NaH COs, which is quickly converted to 02 (Swick and Ip, 1974). 

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