Enzyme preparations obtained from sonically-treated washed cells of Streptococcus mutans strain GS5 were found to contain ‘sucrase’ activity which was distinct from that of the glucosyl and fructosyl transferases known to be elaborated by this organism. This ‘sucrase’ activity was formed constitutively and could be separated from transferase activity by agarose chromatography. The enzyme appears similar, if not identical, to invertase on the basis of its catalytic action, its molecular size, and its heat sensitivity. Its presence in cells of Strep, mutans strain GS5 indicates that this organism is not solely dependent upon the glucosyl and fructosyl transferases for the utilization of sucrose for growth. The total observable ‘sucrase’ activity of glucose grown cells of Strep, mutans strains GS5 and 6715 was found to increase markedly when the organisms were treated with toluene, indicating they were relatively impermeable to sucrose. Untreated sucrose grown cells exhibited 10-fold higher total ‘sucrase’ activity than did untreated glucose grown cells, suggesting that growth in sucrose broth resulted in the induction of a sucrose transport system.

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Rest (201) Tl imaging has been used for detecting viability, but the ideal timing for imaging after injection to maximally estimate viability is not well established. Thirty patients with fixed or incompletely reversible defects on 4 h redistribution SPECT imaging after thallium rest injection underwent 24 h imaging. Global redistribution was subjectively rated none, minimal or meaningful by two experienced observers. Fourteen patients had no meaningful redistribution at either 4 h or 24 h. Ten patients had meaningful redistribution at 4 h only. Six patients had no meaningful redistribution at 4 h but did at 24 h. Defect size was quantified using a 70% threshold. For the total group, defect size was smaller at 4 h compared to immediate imaging (38+/-18% vs 41+/-19%, P=0.06) and smaller still at 24 h (36+/-16% vs 38+/-18%, P=0.02). Later (24 h) redistribution images detected additional redistribution in 30% of the patients who did not have meaningful redistribution on early (4 h) images, and in 8% of the segments which were abnormal at 4 h. It is concluded that, in patients who have incompletely reversible defects on early redistribution imaging at 4 h, late redistribution imaging after 24 h will demonstrate additional redistribution in 30% of the patients.

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