Molybdenum cofactor (Moco) is a prosthetic group necessary for the activity of four unique enzymes, including the essential sulfite oxidase (SUOX-1). Moco is required for life; humans with inactivating mutations in the genes encoding Moco-biosynthetic enzymes display Moco deficiency, a rare and lethal inborn error of metabolism. Despite its importance to human health, little is known about how Moco moves among and between cells, tissues, and organisms. The prevailing view is that cells that require Moco must synthesize Moco de novo. Although, the nematode Caenorhabditis elegans appears to be an exception to this rule and has emerged as a valuable system for understanding fundamental Moco biology. C. elegans has the seemingly unique capacity to both synthesize its own Moco as well as acquire Moco from its microbial diet. However, the relative contribution of Moco from the diet or endogenous synthesis has not been rigorously evaluated or quantified biochemically. We genetically removed dietary or endogenous Moco sources in C. elegans and biochemically determined their impact on animal Moco content and SUOX-1 activity. We demonstrate that dietary Moco deficiency dramatically reduces both animal Moco content and SUOX-1 activity. Furthermore, these biochemical deficiencies have physiological consequences; we show that dietary Moco deficiency alone causes sensitivity to sulfite, the toxic substrate of SUOX-1. Altogether, this work establishes the biochemical consequences of depleting dietary Moco or endogenous Moco synthesis in C. elegans and quantifies the surprising contribution of the diet to maintaining Moco homeostasis in C. elegans.

钼辅助因子 (Moco) 是四种独特酶活性所必需的辅基，包括必需的亚硫酸盐氧化酶 (SUOX-1)。Moco是生活所必需的；在编码 Moco 生物合成酶的基因中具有失活突变的人类表现出 Moco 缺陷，这是一种罕见且致命的先天性新陈代谢错误。尽管它对人类健康很重要，但人们对 Moco 如何在细胞、组织和生物体之间移动知之甚少。普遍的观点是需要 Moco 的细胞必须从头合成 Moco。虽然，线虫秀丽隐杆线虫似乎是该规则的例外，并且已成为了解基本 Moco 生物学的有价值的系统。秀丽隐杆线虫具有看似独特的能力，既可以合成自己的 Moco，也可以从其微生物饮食中获取 Moco。然而，来自饮食或内源性合成的 Moco 的相对贡献尚未经过严格的生化评估或量化。我们从基因上去除了秀丽隐杆线虫中的饮食或内源性 Moco 来源并通过生化方法确定了它们对动物 Moco 含量和 SUOX-1 活性的影响。我们证明饮食中的 Moco 缺乏会显着降低动物 Moco 含量和 SUOX-1 活性。此外，这些生化缺陷会产生生理后果；我们表明，仅膳食 Moco 缺乏会导致对亚硫酸盐（SUOX-1 的有毒底物）的敏感性。总而言之，这项工作确定了消耗秀丽隐杆线虫中的膳食 Moco 或内源性 Moco 合成的生化后果，并量化了饮食对维持秀丽隐杆线虫 Moco 稳态的惊人贡献。