Radioactivity optimum specific activity

Fig.3 shows that the synthesis of Ptd-choline from endogenous Ptd-ethanolamine and added radioactive SAM is lacking at pH values lower than 6, and that it possesses an optimum pH around 8.2. Interestingly, a smaller but consistent pH optimum at about 7 is also present. On examining the incorporation rate of SAM into PDE (Fig.4) similar results were obtained although the specific activities reached were lower. The influence of pH upon the synthesis of BIE is shown in Fig 5 the smaller optimum of activity around pH 7 is no more evident and only the optimum at about pH 8.2 is present. 

Many of the review articles cited above emphasize the sensitivity limits of activation analysis. Experimenters constantly seek techniques to improve these limits for example, a number of recent reports show that some experimenters consider very short-lived species (with radioactive half-lives of seconds or minutes) to be most easily used to obtain sensitivity and a rapid analysis (18,171,177,565,625,883). Other reports (17, 70,157,326,328,461,566,730,832) give specific information about optimum conditions for sensitivity, and other experimenters have evaluated the maximum sensitivity that can be obtained in the presence of interfering radionuclides, a condition that sometimes becomes a major disadvantage in the application of activation analysis methodology to a given sample material (404,729,730,740). 

In many respects the glucosyltransferase was similar to the galactosyl-transferase from the same tissue. It had a pH optimum at 7.4, a Km value for UDP-glucose of 3.1 X 10 M, and required Mn " for full activity. Mn " could be partially replaced by Mg " , Ca ", Ni" ", Co" , and Zn ". The appearance of a major unidentified radioactive product upon addition of Co" has already been mentioned and emphasizes the desirability of an assay procedure that is as specific as possible. TDP- and CDP-glucose could partially replace UDP-glucose, while GDP- and ADP-glucose were inactive. 

---