Abstract
A reexamination of the role of the vermilion cistron (v: 1–33.0) in the control of tryptophan pyrrolase in Drosophila melanogaster uncovered several, previously unknown features about this enzyme: 1. Crude extracts of Drosophila possess one or more inhibitors which may be removed by Norit treatment during homogenization. 2. Contrary to previous assertion, crude wild type extracts are stimulated by an exogenous source of hematin, and upon purification, become heavily dependent upon added methemoglobin. 3. The wild type enzyme exhibits a lag period in time course of product accumulation which is eliminated by preincubation with methemoglobin and α-methyltryptophan. 4. The molecular weight of the wild type enzyme is estimated at approximately 150000 Daltons. 5. A linear increase of tryptophan pyrrolase activity as a function of dosage of v+ alleles supports the contention that the vermilion cistron is the structural gene for this enzyme. 6. A sex difference in response to gene dosage (dosage compensation) is seen.
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