Sanford Y M, Orias E
Proc Natl Acad Sci U S A. 1981 Dec;78(12):7614-8. doi: 10.1073/pnas.78.12.7614.
Nineteen tyrosine auxotrophs of the ciliated protozoan Tetrahymena thermophila have been isolated and biochemically examined. These mutants are defective in the conversion of phenylalanine to tyrosine; this is analogous to the defect that causes phenylketonuria in humans. After nitrosoguanidine mutagenesis and self-fertilization, progeny clones were screened for tyrosine auxotrophy and positively identified by using growth tests and in vivo radiometric assays for phenylalanine-to-tyrosine conversion. Mutants in one complementation group (locus) lacked phenylalanine hydroxylase activity; mutants in three other loci appeared to be deficient in the unconjugated pteridine cofactor that is necessary for the function of the hydroxylase. Another mutant lacked the dihydropteridine reductase activity required to regenerate the reduced form of the pteridine cofactor. Because hydroxylation of tyrosine to dopa and of tryptophan to 5-hydroxytryptophan may require the same cofactor and pterin reductase as phenylalanine hydroxylase, these mutants may also prove useful for the study of the role of catecholamines and serotonin, substances known to be present in Tetrahymena.
已分离出19株嗜热四膜虫的酪氨酸营养缺陷型，并对其进行了生化检测。这些突变体在苯丙氨酸向酪氨酸的转化过程中存在缺陷；这类似于导致人类苯丙酮尿症的缺陷。经亚硝基胍诱变和自体受精后，通过生长试验和体内苯丙氨酸向酪氨酸转化的放射性测定法筛选子代克隆，并进行酪氨酸营养缺陷型的阳性鉴定。一个互补群（位点）中的突变体缺乏苯丙氨酸羟化酶活性；其他三个位点的突变体似乎缺乏羟化酶功能所需的未结合蝶啶辅因子。另一个突变体缺乏再生蝶啶辅因子还原形式所需的二氢蝶啶还原酶活性。由于酪氨酸向多巴的羟化以及色氨酸向5-羟色氨酸的羟化可能需要与苯丙氨酸羟化酶相同的辅因子和蝶呤还原酶，这些突变体可能也有助于研究儿茶酚胺和血清素的作用，已知嗜热四膜虫中存在这些物质。
