Determination of amino acid production rate of a marine phytoplankton population with 13C and gas chromatography‐mass spectrometry1

Abstract

Combined 13C and gas chromatography ‐mass spectrometry (GC‐MS) were applied to determine the rate of amino acid production of marine phytoplankton populations. The accuracy of the estimate of the 13C ratio in each amino acid using the relative intensity of isotope peaks was investigated with 13C‐enriched amino acid standards. Production rates of 12 amino acids of a natural phytoplankton population were determined. The gross amino acid composition of photosynthetic products is generally comparable with previous reports. Production of amino acid at night was confirmed by the increase in 13C atom%; glucose appeared to supply carbon for amino acid production at night. The ratio of carbon : amino acid nitrogen in photosynthetic products showed a marked diurnal change, due mainly to the loss of glucose carbon at night and the continuing uptake of nitrogen.

Production and neutral aldose composition of dissolved carbohydrates excreted by natural marine phytoplankton populations

“…The 13 C atom% of each NAld was estimated from the differences in the relative intensities of isotopic peaks between nonincubated and incubated samples (Kouchi 1982;Hama and Handa 1986). The detailed analytical conditions of GC and GC/MS can be found in Hama et al (1987).…”

“…where a is is the 13 C atom% in an incubated sample, a ns is the 13 C atom% in a natural (nonincubated) sample, a ic is the 13 C atom% in inorganic carbon, t is the incubation length (h), and [C]: concentration (gC L Ϫ1 ) of POC or NAld in the incubated sample. The coefficient of variation of the determination of the photosynthetic production rate is generally within 5% (Hama et al 1993). Equation 1 is also applied to the calculation of the production rates of DOC and DNAld by excretion, but [C] is the concentration of DOC or DNAld in the incubated sample.…”

“…In natural environments, on the other hand, the measurement of the concentration of organic compounds in the ambient waters by GC or HPLC can not distinguish materials freshly produced by phytoplankton from ambient DOM. Hama et al (1987) applied a combination of a 13 C tracer technique with GC/mass spectrometry (GC/MS) to determine the production rate of organic molecules, such as monosaccharides of carbohydrates and amino acids of proteins, in the photosynthetic products of phytoplankton. When this method is applied to the study of the production process of DCHO, the production rates of the monosaccharides from phytoplankton excretion that constitute DCHO can be measured.…”

“…When this method is applied to the study of the production process of DCHO, the production rates of the monosaccharides from phytoplankton excretion that constitute DCHO can be measured. Further, the isotopic ratio, which is measured for particular elements (C in the present study) and organic molecules in the stable isotope tracer technique, involves the combined information of concentration and production rates (Dugdale and Goering 1967;Hama et al 1993). Thus, the turnover rates of DOC and monosaccharides of DCHO through phytoplankton excretion can be estimated and make it possible to compare the biogeochemical properties of DOC and DCHO at the molecular level.…”

Effect of nitrate-N incorporation on the composition of the intracellular amino acid pool of N-deprivedTetraselmis marina

“…2) when subjected to N-deprivation in darkness. Such differences must reflect varying abilities to synthesize amino acids, and hence protein, in darkness (Smith, Bassham & Kirk, 1961;Hipkin et al, 1982) and also affects the use of estimates of amino acid production using a sC methods (Hama, Handa & Hama, 1987). Since much algal protein is thought to be synthesized at night using energy from carbohydrates and lipid synthesized during the day (Cuhel, Ortner & Lean, 1984), fluctuations in the quantitative and/or qualitative composition of the amino acid pool are to be expected in N-replete cells growing in natural conditions.…”