Abstract
In the course of experiments to determine what factors in a rabbit's diet are essential to virus multiplication it was observed that the subcutaneous injection of methionine increased the rabbit's resistance to dermal infection with vaccinia. Six experiments have been performed with methionine. The results of a typical experiment are shown in Table I. In this experiment and others described below rabbits weighing approximately 2 kg were used. The experimental rabbits received 300 mg of methionine subcutaneously daily for 2 days preceding and 5 days following vaccination. In other experiments the conditions of the experiment were varied as to the amount of methionine and the times at which it was given. These experiments showed that if the methionine was given 48 hr before vaccination, the resistance was increased 14 fold; if given immediately following vaccination, the increase was 10 fold; if delayed until 48 hr after vaccination the increase was 5 fold. In addition to these quantitative changes in resistance, the lesions of the animals whose resistance had been stimulated most by methionine were smaller and disappeared approximately 24 hr earlier than did the ones of the control animals. Measurements of resistance were made by use of serial dilutions of vaccinia virus as described previously. 1 The experimental error in this method is considerably less than a 2-fold difference, hence the observed changes were highly significant.
Additional studies were than undertaken to determine what biological functional group of the methionine molecule was responsible for this effect. That it was probably not dependent on the generalized properties of the amino acids as such was indicated by the fact that glycine had no significant effect on susceptibility. Neither does the mere presence of sulfur in the molecule explain the action, for cystine did not duplicate the effect of methionine.
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