Among 28 groups of eukaryotes, apart from Metazoa, phosphagen kinase (PKs) is distributed in only a few protist groups, including the Choanomonada with the closest affinity to metazoans. To clarify the origin of metazoan PKs, we performed a database search and focused on 11 sequences of PK homologs from five groups of protists: the Choanomonada, Alveolata, Haptophyta, Stramenopiles, and Cryptophyta. The recombinant enzymes were prepared to determine their substrate specificity. Emiliania (Haptophyta), Anophryoides, Pseudocohnilembus, Vitrella and Chromera (Alveolata), and Monosiga (Choanomonada) all contained a gene for arginine kinase (AK). In contrast, Aphanomyces, Albugo and Ectocarpus (Stramenopiles), and Guillardia (Cryptophyta) possessed a gene for taurocyamine kinase (TK). The Guillardia TK enzyme exhibited rather strong substrate inhibition toward taurocyamine, which was analyzed using the most likely kinetic model. This was the first report of substrate inhibition in a TK. Together with the research results from other groups, the AK, TK, or creatine kinase (CK) activities have been observed sporadically in at least six groups of protists. However, it is not clear the three enzyme activities were emerged early in the evolution and divergence of protist groups, or some of enzyme activities were introduced to the protists by horizontal gene transfer. In addition, we found that seven protist enzymes examined in this study possess a myristoylation signaling sequence at the N-terminus.

The amino-acid sequence around the guanidine-specificity region and the key residue at 89^th position of the protist AK and CK were homologous to those of the metazoan enzymes, but those for protist TKs were different indicating that the latter evolved independently.

在 28 类真核生物中，除后生动物外，磷酸原激酶 (PKs) 仅分布在少数原生生物群体中，包括与后生动物亲和性最接近的 Choanomonada。为了阐明后生动物 PK 的起源，我们进行了数据库搜索，并专注于来自五组原生生物的 11 个 PK 同源物序列：Choanomonada、Alveolata、Haptophyta、Strmenopiles 和 Cryptophyta。制备重组酶以确定它们的底物特异性。Emiliania (Haptophyta)、Anophryoides、Pseudocohnilembus、Vitrella and Chromera (Alveolata) 和Monosiga (Choanomonada) 都含有精氨酸激酶 (AK) 基因。相比之下，Aphanomyces、Albugo和Ectocarpus (Stramenopiles) 和Guillardia (Cryptophyta) 拥有牛磺胺激酶 (TK) 基因。吉拉迪亚_TK酶对牛磺氰胺表现出相当强的底物抑制作用，使用最可能的动力学模型对其进行分析。这是 TK 中底物抑制的第一份报告。连同其他组的研究结果，至少在六组原生生物中偶尔观察到 AK、TK 或肌酸激酶 (CK) 活性。然而，尚不清楚这三种酶活性是在原生生物群的进化和分化早期出现的，或者是通过水平基因转移将一些酶活性引入原生生物。此外，我们发现本研究中检测的七种原生生物酶在 N 末端具有豆蔻酰化信号序列。

原生生物AK和CK的胍特异性区域周围的氨基酸序列和第89位的关键残基^与后生动物的酶同源，但原生TK的氨基酸序列不同，表明后者独立进化。