N^1'-Methylthiaminium Diiodide. Model Study on the Effect of Coenzyme Bound Positive Charge on Reaction Mechnism Requiring Thiamin Pyrophosphate (Journal of the American Chemical Society (1978) 100(8) (2534–2541)(10.1021/ja00476a043))

1. In Table III under decarboxylation the numbers should be changed to read as (a change only in all four exponents from 1CT6 [formula omitted] to 1CT3). Although these results have been reproduced, the pH-stat technique employed is not following decarboxylation rates ex- clusively since somewhat similar results could be obtained sub- stituting equimolar acetate for pyruvate at the same pH. On account of this ambiguity Figure 4 and the accompanying first paragraph under Results and Discussion (Decarboxylation and Acetoin Formation) should be disregarded. Very likely what was being monitored by pH-stat was a combination of reactions related to the chemistry of thiamin as catalyzed by pyruvate, as well as pyruvate decarboxylation catalyzed by thiamin. This negative experience with the pH-stat method warns us not to employ this method in model pyruvate decarboxylation rate studies. 2. The raw data presented for thiazolium ring opening in Figure 5 is correct but a factor of 2.3 (from log to In) was inadvertantly left out in the calculation of kohs in Table III. That row in Table III should now read as follows: Thiazolium ring opening; temp, °C, 30 ± 1; pH, 9.6 ± 0.1; kobsd with la, 1.3 X 10“3 s“1; Kobsd with lb, 5.1 X 10~3 s“1; concn., 10~4 M; rel rates, rate Ib/rate la, 3.9. Since the manuscript emphasized the relative rates obtained with la and lb, the conclusions are not affected in any way. The authors thank Dr. R. Kluger, University of Toronto, for bringing to their attention the problem discussed in paragraph 1.