Section 4 — Gene Action 



but Esterase 6 activities of the various strains and 

 of offspring from crosses, will be presented in an 

 attempt to show whether or not the two systems 

 are interrelated. 



1. Botyu-Kagaku, Scientific Insect Control 26, 

 93, 1961. 



2. Amer. Zool. 1, 476, 1961. 



4.32. In Vitro Interconversion between Mutant Forms 

 of the pH 7.5 Esterase in Maize. Drew 

 Schwartz (Cleveland, U.S.A.). 



Six esterase isozymes distinguished by elec- 

 trophoretic mobility are formed by the three 

 alleles of the E locus in maize. Three isozymes 

 FF S NN and SS are formed by the E F , E N and 

 E s alleles when in homozygous condition and in 

 addition three hybrid isozymes FN, NS, FS 

 occur in the three heterozygous combinations. 

 The FS hybrid isozyme migrates at the same rate 

 as the NN band. Recent results indicate that the 

 difference in the migration rates between the 

 isozymes are due to a positively charged group 

 associated with the enzyme. By treating extracts 

 with sodium borohydride, the single pH 7.5 

 esterase band found in homozygotes is converted 

 into a series of bands, all less positively charged. 

 These new bands show migration rates identical 

 to those produced by the various E alleles in 

 homozygous and heterozygous combinations. In 

 addition a new band migrating slower than the 

 SS band is also seen. Treatment of FF extracts 

 yields bands which are electrophoretically in- 

 distinguishable from the FF, FN, NN (or FS), 

 NS and SS isozymes. Treatment of NN extracts 

 reveals four bands, NN, NS, SS, and the new 

 slow band. Treatment of the SS extracts yields 

 only two bands, the SS and the new slow band. 

 When a mixture of E F /E N and E N /E S extracts 

 which contain all five isozyme types are treated, 

 no new bands are seen except for that at the new 

 slow position. These data are consistent with the 

 hypothesis that F, N and S are associated with 

 decreasing numbers of the positive charge group 

 and that sodium borohydride removes varying 

 numbers of the charged groups thereby convert- 

 ing the more positively charged isozymes into 

 the less positively charged enzyme types. The 

 other esterases and proteins in the same extracts 

 are not effected by the borohydride. 



4.33. Two Forms of Tyrosinase from Each of Two 

 Different Mouse Melanomas. Jean B. Burnett 

 and George F. Wilgram (Boston, U.S.A.). 



The early work of Brown and Ward which 

 resulted in the preparation of a soluble tyrosinase 

 from mouse melanotic tumor has been the basis 

 for current studies leading to the further puri- 

 fication and elucidation of the properties of this 

 enzyme. 



Harding-Passey and B-16 tumors are grown 

 in Swiss white and C-57 black mice respectively. 

 Harding-Passey and B-16 tumors each contain 

 tyrosinases which are electrophoretically sepa- 

 rable into two components; Ta, a tyrosinase of 

 greater anodic mobility and T|, a tyrosinase of 

 lesser anodic mobility. At pH 8.6, T a (H-P) and 

 T* (B-16) are tyrosinases of identical mobility 

 while T^ (H-P) and Tf (B-16) are tyrosinases of 

 also identical but of lesser anodic mobility. T£ 

 and T| of both tumors are also separable by 

 column chromatography. An additional purifi- 

 cation o fapproximately 10-fold is obtained using 

 a DEAE-Sephadex ion exchange column. Cha- 

 racteristically, the enzymes have the same 

 Michaelis constant and maintain characteristic 

 differences in specific activity during the course 

 of purification. Tryptic or chymotryptic digests 

 of the purified enzymes (i.e. fingerprinting) 

 suggest differences in amino acid sequence and 

 composition. 



These properties of the tyrosinases suggest 

 that differences in primary structure are most 

 likely in the inactive protein moiety of the en- 

 zyme while the primary, and probably tertiary, 

 structure of the active sites are the same or very 

 similar. 



4.34. Studies on the Biosynthesis of Tyrosinase in 

 Neurospora. Helen Macleod, Marguerite 

 Fling, and N. H. Horowitz (Pasadena, 

 U.S.A.). 



The tyrosinase of TV. crassa is a crystallizable, 

 copper-containing enzyme of molecular weight 

 30-35,000. It has been the subject of a number 

 of genetic and biochemical studies. (*) The en- 

 zyme is not produced in rapidly growing cultures, 

 but is formed during the sexual phase of the life 

 cycle, or in vegetative cultures when growth is 

 inhibited by starvation or by amino acid analogs 

 (e.g. ethionine, fluorophenylalanine, D-aromatic 

 amino acids). When wild-type cultures growing 

 on minimal medium are starved by transferring 

 them to phosphate buffer, tyrosinase synthesis 

 starts after a lag period, attains its maximal rate 

 at about 24 hr after transfer, and ceases at about 

 60 hr after transfer. At this time, tyrosinase con- 

 stitutes from 1 to 5 per cent of the extractable 

 proteins. This induction of tyrosinase synthesis is 

 much reduced in a mutant (ty-1) which is not 



47 



