Soil microbes release a variety of aminopeptidase enzymes to degrade proteins into their constituent amino acid monomers, thereby increasing amino acid availability in the near-cell environment. We investigated how inorganic N availability controls the substrate induction response of aminopeptidase enzymes by conducting protein amendment experiments via gelatin addition to fertilized and unfertilized soil from a long-term N addition study. Protein addition triggered a measurable increase in enzyme activity, which we interpreted as an induction response, in all five of the aminopeptidase enzymes we investigated. The magnitude of these induction responses did not differ by fertilization regime even when unamended aminopeptidase activity differed between long-term fertilization treatments. Though soil microbes are thought to release aminopeptidase enzymes as a means of cellular N acquisition at steady-state concentrations, our results suggest that they use the same enzymes to access protein-derived C as an energetic resource at non-steady-state conditions, such as those triggered by the substrate induction response. The substrate induction response of aminopeptidase enzymes is therefore best viewed as a means of microbial competition for the substantial energetic resources available in protein subsidies.

土壤微生物释放出各种氨肽酶，以将蛋白质降解成其组成的氨基酸单体，从而增加了近细胞环境中氨基酸的利用率。我们通过一项长期的添加研究，通过将明胶添加到受精和未施肥的土壤中进行明胶添加实验，研究了无机氮的有效性如何控制氨基肽酶的底物诱导反应。在我们研究的所有五种氨肽酶中，蛋白质的添加引发了酶活性的可测量增加，我们将其解释为诱导反应。即使长期施肥之间未修饰的氨肽酶活性不同，这些诱导反应的幅度也因施肥方式而不同。尽管土壤微生物被认为是在稳态浓度下释放氨肽酶的一种手段，以获取细胞中的氮，但我们的研究结果表明，它们在非稳态条件下使用相同的酶来获取蛋白质衍生的C作为能量资源，例如如由底物感应响应触发的那些。因此，最好将氨基肽酶的底物诱导反应视为微生物竞争蛋白质补贴中可利用的大量能量资源的一种手段。