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ALTERED PTERIN PATTERNS IN PHOTOBEHAVIORAL MUTANTS OF Phycomyces blakesleeanus *
Author(s) -
Hohl Norbert,
Galland Paul,
Senger Horst
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb04233.x
Subject(s) - phycomyces , biopterin , pterin , mutant , phycomyces blakesleeanus , biochemistry , wild type , biology , chemistry , gene , cofactor , enzyme , tetrahydrobiopterin
— Pterins were extracted with methanol from sporangiophores of the lower fungus Phycomyces blakesleeanus and separated and identified by high performance liquid chromatography (HPLC) with fluorescence detection. The following pterins were found and identified for the wild‐type strain NRRL1555: carboxypterin (6.7 × 10 ‐6 M ), neopterin (4.2 × 10 ‐7 M ), xanthopterin (5.3 × 10 ‐6 M ), biopterin (3.9 × 10 ‐7 M ), pterin (9.1 × 10 ‐7 M ), and 6,7‐dimethylpterin (1.2 × 10 ‐6 M ). The HPLC elution profiles of the wild type were compared to a set of phototropism mutants (genotype mad ) with specific defects in the light‐transduction pathway. The mutant profiles were qualitatively similar to those of the wild type. Quantitative differences were, however, discerned for madA, madC , and madH mutants. The madA mutation was associated with increased amounts of biopterin and 6,7‐dimethylpterin and a reduction of neopterin, pterin, xanthopterin, and unidentified pterins eluting at 14–18 min. The stimulatory effect of the madA mutation on biopterin and 6,7‐dimethylpterin appears to be compensated by a secondary mutation ( pde ) which is responsible for the loss of 75% of adenosine 3',5'‐cyclic monophosphate (cAMP)‐phosphodiesterase activity. In a madA pde double mutant the amounts of biopterin and 6,7‐dimethylpterin fell below the wild‐type level. These results suggest that an increased level of endogenous cAMP represses the biosynthesis of these pterins. The madC mutation increased the amounts of biopterin and xanthopterin and that of the unidentified pterins which could be derivatized to carboxypterin. Single madB mutations had, compared to the wild type, two times higher amounts of biopterin and two times lower amounts of neopterin. In a madH mutant the identified pterins occurred at normal concentrations while the total pool of pterins and of unidentified pterins were elevated. Complex changes of the pterin pattern were obtained in various double mad ‐mutants suggesting that some mad gene products synergistically control the pterin content. The results of this and the accompanying paper (Hohl et al. , 1992, Photochem. Photobiol. 55 ) show that some of the mad genes affect pterin as well as flavin levels in Phycomyces. We propose that photoreception of Phycomyces requires a balanced and precisely controlled ratio of endogenous pterins and flavins. For some of the mutants the relative excess of certain pterins may cause the known sensitivity changes in the near‐UV.