Hydrolysis of Adenosine Triphosphate by Conventional or Microwave Heating
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HYDROLYSIS OF ADENOSINE TRIPHOSPHATE BY CONVENTIONAL OR MICROWAVE HEATING EDWIN G. E. JAHNGENt, RONALD R. LENTZ t, PETER S. PESHECK t, AND PATRICIA HOLT SACKET-rt * Department of Chemistry, University of Lowell, Lowell, MA 01854.
t
The Pillsbury Company, Research and Development Laboratories, 311 2nd St., S.E., Minneapolis, Minnesota 55414.
ABSTRACT The hydrolysis rate of adenosine-5'-triphosphate (ATP) has been reported to be 25 times greater during microwave heating than during conventional heating at comparable temperatures (100 to 105 'C). This remarkable rate increase was both attributed to and cited as evidence for a nonthermal microwave effect. Attempts to replicate those findings under carefully controlled microwave exposure conditions and with special attention being paid to accurate temperature measurements lead to the conclusion that the hydrolysis rate is related solely to temperature. INTRODUCTION Sun et al. [1) recently reported that the hydrolysis rate of adenosine-5'triphosphate (ATP) was 25 times greater during microwave heating than during conventional heating at comparable temperatures (100 to 105 *C). This remarkable rate increase was both attributed to and cited as evidence for a nonthermal microwave effect. In the present paper, ATP hydrolysis reaction kinetics determined from conventionally heated samples have been used in conjunction with temperatures measured in microwave heated samples to calculate predicted final concentrations of ATP in the microwave heated samples. Those calculated concentrations are then compared with measured ATP concentrations in microwave exposed samples to see if conventionally determined kinetics adequately explain the results of microwave heating. CONVENTIONAL HEATING Following [1], 1 mM solutions of ATP in 0.01 M KH 2 PO 4 , adjusted to pH 6.8 with base, were used as standards and for exposure to heat as samples. Samples were heated in borosilicate glass tubes, cut 10 cm long from 3.9 mm OD (2.3 mm ID) glass and sealed at one end with a gas torch. Samples were sparged 15 minutes with helium and added to fill the tubes to 3.4-3.9 cm (0.14-0.16 mL). The open end was then sealed, and tubes refrigerated before and after exposure to minimize ambient hydrolysis. Prepared samples were randomly selected for microwave or conventional heating. Conventional reaction kinetics were determined by exposing a series of samples for 10 min to fixed oil bath temperatures between 90 and 125 *C at 5 °C intervals. The temperature at the center of samples immersed in the oil bath rose to within 10 *C of the bath temperature in 15 seconds and to within 2 °C in 30 seconds. Mat. Res. Soc. Symp. Proc. Vol. 189. @1991 Materials Research Society
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As bath temperature increased, a regular decrease in ATP was seen along with a gradual increase in adenosine-5'-diphosphate (ADP) with an eventual plateau and dropoff, and a steady increase of adenosine-5'-monophosphate (AMP) concentration (Figure 1). Attention has been mainly confined to the decay of ATP to ADP by first order reaction kin
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