ABSTRACT: Leucine aminopeptidase (LAP) is one of the enzymes involved in the hydrolysis of peptides, and is sometimes used to indicate potential nitrogen limitation in microbes. Small-scale variability has the potential to confound interpretation of underlying patterns in LAP activity in time or space. An automated flow-injection analysis instrument was used to address the small-scale variability of LAP activity within contiguous regions of the Hudson River plume (New Jersey, USA). LAP activity had a coefficient of variation (CV) of ca. 0.5 with occasional values above 1.0. The mean CVs for other biological parameters—chlorophyll fluorescence and nitrate concentration—were similar, and were much lower for salinity. LAP activity changed by an average of 35 nmol l^-1 h^-1 at different salinities, and variations in LAP activity were higher crossing region boundaries than within a region. Differences in LAP activity were ±100 nmol l^-1 h^-1 between sequential samples spaced <10 m apart. Variogram analysis indicated an inherent spatial variability of 52 nmol l^-1 h^-1 throughout the study area. Large changes in LAP activity were often associated with small changes in salinity and chlorophyll fluorescence, and were sensitive to the sampling frequency. This study concludes that LAP measurements in a sample could realistically be expected to range from zero to twice the average, and changes between areas or times should be at least 2-fold to have some degree of confidence that apparent patterns (or lack thereof) in activity are real.

中文翻译：

---

定量水生氨肽酶活性的小规模异质性

摘要：亮氨酸氨基肽酶（LAP）是参与肽水解的酶之一，有时被用来指示微生物中潜在的氮限制。小规模的变异有可能混淆时间或空间中LAP活动中潜在模式的解释。使用自动流动注射分析仪解决了哈德逊河羽流（美国新泽西州）连续区域内LAP活性的小规模变化。LAP活性的变异系数（CV）为ca。0.5，偶尔值大于1.0。其他生物学参数（叶绿素荧光和硝酸盐浓度）的平均CV相近，而盐度则低得多。LAP活性平均变化35 nmol l ^-1 h ^-1在不同的盐度下，LAP活性的变化跨区域边界要高于区域内。间隔小于10 m的连续样本之间的LAP活性差异为±100 nmol l ^-1 h ^-1。变异函数分析表明52 nmol l ^-1 h ^-1的固有空间变异性整个研究区域。LAP活性的大变化通常与盐度和叶绿素荧光的小变化有关，并且对采样频率敏感。这项研究得出的结论是，实际上可以预期样品中的LAP测量值在平均值的零到两倍之间，并且面积或时间之间的变化至少应为2倍，以确保在某种程度上可以确定表观模式（或缺乏模式）。活动是真实的。