| First Author | Cumming RB | Year | 1977 |
| Journal | Mouse News Lett | Volume | 56 |
| Pages | 53-4 | Mgi Jnum | J:13710 |
| Mgi Id | MGI:61891 | Citation | Cumming RB, et al. (1977) A structural gene for formamidase. Mouse News Lett 56:53-4 |
| abstractText | Full text of MNL contribution: Research News: A. A structural gene for formamidase. Formamidase (kynurenine formamidase, aryl -formylamine amidohydrolase, EC 3.5.1.9) is the second enzyme in the pathway of tryptophan degradation. It catalyzes the reaction: N-formyl-L-kynurenine + L-kynurenine + formate. This enzyme has been studied in a number of organisms and has been purified from several, but no genetics has been developed for its production or control. The assay for formamidase is simple (monitoring the production of product, kynurenine, with time at 365 nm), and it lends itself readily to the GeMSAEC centrifugal rapid analyzer technology under continuing development in the Chemical Technology Division of ORNL. Using this system we have done about 3000 formamidase assays in the past three months on the enzyme from mice and the results to date, though still very incomplete, are summarized as follows: 1. There are two distinct formamidase phenotypes among the liver homogenates of different inbred strains of mice. Some strains (including 129, DBA, CFCW, CFW, C3Hf, A, 101, RFM and T-stock) show high activity of ~ 30 I.U. per gram o f 1 i v e r tissue. Other strains (including BALB/c, SEC, SEA, C57BL10/Sc Sn, C57BI6, C57BR, C57L and C57BL10-Sp) have low activity of ~ 10 I.U. per gram of liver tissue. There are no intermediates among the strains we have tested, but F1 hybrids between C57BL10 and C3Hf show an activity exactly intermediate between the two parental strains (~ 20 I.U./g). There is no influence of sex on enzyme activity. 2. During partial purification procedures for mouse formamidase, two separate peaks of activity elute from DEAE cellulose columns in both high (C3Hf) and low (C57BL10) strains. These are different enzyme proteins both chemically and genetically. The first (minor) peak appears to have the same activity in both high and low strains and has a very high Km for formyl kynurenine (about 50 mM). The second (major) peak accounts for a1l of the difference in activity between high and low strains, and has a much lower Km for the same substrate (about 0.15 mM). 3. In crosses between C3Hf and C57BL10, F1Õs are intermediate in activity, as indicated earlier. Data from F2's and backcrosses of F1Õs to both parental strains show that high and low activities segregate as a single autosomal Mendelian additive factor. The locus is not linked to sex and is not linked to the a locus which also segregates in these crosses. No other linkage data are presently available though this problem is under study. 4. Heat inactivation profiles and other preliminary biochemical data indicate that the alleles for the low Km enzyme, which segregate genetically, code for different molecular forms of formamidase in the high and low strains. Therefore, the locus involved is the structural gene for the enzyme and not some second site control locus. 5. Formamidase activities in the last three days of fetal life are about 10% of adult activities for both high and low strains. There is about a two-fold increase in activity at birth;and thereafter enzyme activity increases slowly, reaching adult levels in low strains (C57BL10) at about 12 days of age and in high strains (C3Hf) at about 50 days of age. From the above considerations we propose to name the structural locus for formamidase I in the mouse (the second and major peak of formamidase activity to elute from DEAE cellulose) For-1. This locus has two known alleles: For-la, which is characterized by high total 1iver formamidase activity and a very much more heat stable enzyme and is found in C3Hf/RL and For-lb, which i s characterized by lower activity and a more heat labile enzyme and is found in C57BL10/Sn Sc (obtained in this laboratory from Cudcowicz in 1965). It is now thought that the strains listed at the beginning of this report with high activity have the For-la allele and that strains listed with low activity have the For-1b allele, but further testing will be necessary to prove this point. (R. B. Cumming, F. H. Gaertner, Marva F. Walton and Sean C. 0' Donne1l.) |
