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The effect of high dose ascorbate on urinary oxalate levels in healthy adults was investigated using a modified ion chromatography method. Subjects ingested 1, 5 and 10 gm. supplemental ascorbate per day for 5 days, separated by 5 days of no supplementation. Urine ascorbate levels demonstrated variable increases with ascorbate supplementation. Ascorbate added directly to urine in vitro resulted in statistically significant but modest increases in measured oxalate. Addition of 5.68 mmol./l. ascorbate increased measured urinary oxalate by 36 mumol./l., implying conversion of ascorbate to oxalate during analysis. Measurement of 24-hour urinary oxalate levels with 5 and 10 gm. ascorbate per day showed similar, modest increases, which could be entirely accounted for by oxalate production during analytical procedures. Thus, no genuine increase in urinary oxalate was demonstrable despite a greatly increased ascorbate intake.

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The substrate, ATP, protects the active site of cardiac myosin during a 10-min treatment at 37 "C and neutral pH in the absence of divalent cations; under these conditions there is an approximate 20 % dissociation of light chain C1 and 60 % loss of light chain CZ with no corresponding decrease in myosin ATPase activity. Higher temperatures, the absence of divalent cations, increased treatment time, and low protein concentration were conducive to light chain dissociation; loss of light chains did not appear to be influenced by increments of pH from 7.0 to 9.0. On the other hand, a decrease in protein concentration and an increase in both duration of exposure at 37°C and an alkaline pH caused a decrease in myosin ATPase activity. Concomitant with the dissociation of cardiac myosin light chains, particularly light chain C2, there was a corresponding loss in the number of high-affinity calcium binding sites. When the dissociated light chains were recombined with lightchain-deficient myosin, reassociation took place and the number of high-affinity calcium binding sites were regained. Reassociation of light chains with light-chain-deficient myosin did not restore diminished light-chain-deficient myosin ATPase activity. There is a shift in the pH optimum of myosin at 37 "C in the absence of divalent cations, where conditions used for light chain dissociation are employed. The presence of calcium prevents light chain dissociation, helps retain myosin ATPase activity at 37 "C and prevents a shift in the pH optimum.

No abstract