Biochemical Pharmacology. Vol. 28. pp. 3019-3021 & Pergamon Press Ltd. lY7Y. Prmted m tireat Brrtam. 0006.2952!79/1001-3019 SO2.0010 zyxwvuts SHORT COMMUNICATIONS Induction of tyrosine cl-ketoglutarate transaminase by primycin in rat liver zyxwvutsrqponmlk (Received I7 January 1979; accepted 10 April 1979) Primycin is a highly toxic antibiotic with a bacteriostatic effect cm Gram-positive bacteria 1 iI. Its chemical structure was determined by A~rh~dt ef al. I21. Earlier literary data, in an attempt to clarify its mode of action, indicated that primycin inhibits DNA dependent RNA synthesis [31. In 1967, VBlyi-Nagy et al. 131demonstrated that primycin inhibits the glucocorticoid mediated induction of tryptophan 2,3-dioxigenase (EC 1.13.11.11) in rat liver, and concluded by these indirect experiments that primycin, like actinomycin D, inhibits the transcription of the DNA. Recent experiments seem to indicate that the biological effect of primycin could primarily lx attributed to its effect on the membrane [41. It is well documented, that in rat liver, tyrosine aminotrans- ferase responds similarly to tryptopban pyrrolase to gluco- corticoids [ 81. Therefore, similar mechanisms may operate zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH in the regulation of both tyrosine aminotransferase and trypto- phan pyrrolase synthesis. As a working hypothesis, therefore. we sought to investi- gate the effect of primycin on the induction of tyrosine aminotransferase in viva. We found that primycin administered in subtoxic doses causes a 4-S fold increase in tyrosine aminotransferase (TAT) activity in rat liver, while it is practically ineffective on the dexamethasone induced synthesis of the enzyme. Table 1 illustrates the changes in TAT level 6 hr after treatment of animals. As shown, the response of the enzyme to primycin is lower than the response to dexamethasone, but the differences in enzyme level between control and treated animals are significant (P < 0.05). A slight inhibition was observed when primycin and dexamethasone were given together. In compar- ison to dexamethasone induced TAT level, this slight inhibi- tion does not seem signific~t (P > 0.05). The inductive effect of primycin is dose~ependent; a marked increase in TAT activity could already be observed at 0.025 mg/kg, and at 0.250 mg/kg enzyme activity reached a maximum. This value was attained without further increase up to doses of 1.0 mgf kg (Fig. 1). TAT induction could also be observed in adrena- lectomized rats after primycin injection. Actinomycin D and cycloheximide inhibited the induction of TAT by primycin, an indication that the induction involves de nova protein synthesis (Table 1). An increase in tyrosine aminotransferase enzyme protein was further supported by the results obtained upon immuno- titration tests (Fig. 2) where we observed a 4-5 fold increase in TAT enzyme level in the liver extract of induced animals (Fig. 2, panel A). Using the same method we were able to prove that the basal and the induced enzymes are both products of the same gene (Fig. 2, panel B). The contradicting effect of primycin on tyrosine amino- transferase and tryptophan pyrrotase seems to disprove in principle the view taken by Valyi-Nagy et al. /31 that this antibiotic inhibits transcription of DNA into mRNA. These opposing effects on the other hand, and the fact thq primycin causes a 4-5-fold induction in TAT, seem to exclude the possibility that primycin caused induction process is mediated through the adrenal-hypophyseal system. The findings presented above suggest the following hypothesis. (1) Primycin stimulates the TAT enzyme formation by an cd-...- . 0 0.10 0.20 0.30 0.40 0.50 Dose: / kg mg ( Primycin 1 Fig. 1. Dose response of TAT induction by primycin. Primycin in different doses were administered in a single i.p. injection to male Wistar albino rats of 120- 150 g body weight at 8 a.m. Animals were killed 6 hr after the treatment. Preparation of cytosols, and determination of TAT activity was the same as indicated under Table 1. 3019