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Simple correlation and multiple regression analyses were performed to examine the relationship between primary productivity and environmental factors in the north basin of Lake Biwa. The primary production rates used in the analyses were estimated monthly or bimonthly during the growing season (April–November) in 1992, 1996 and 1997 with the 13C method. Elemental (C, N and P) contents of seston were used to assess nutrient conditions. Analyses revealed that 86% of variance in depth‐integrated primary production rates (areal PP) can be explained by changes in light intensity, and sestonic C, N and P concentrations. Water temperature had no effect on areal PP. To assess relative effects of light and nutrients on PP, the P:B ratio was estimated by normalizing PP with sestonic C. The areal P:B ratio correlated most significantly with the sestonic N:P ratio, followed by light intensity. When regression analyses were made at each depth, however, the P:B ratio correlated significantly only with the sestonic N:P ratio at 0 and 1 m depths, while light intensity was also incorporated into the regressions at deeper than 2.5 m. In these regressions, the P:B ratio was negatively correlated with sestonic N:P ratio but positively with light intensity. The results suggest that the primary production rate in this lake was mainly limited by P relative to N supply rates, but was not free from light limitation in a large part of the epilimnion. In Lake Biwa, the vertical water mixing regime as well as the nutrient supply seem to be important in determining the growth and composition of primary producers, since the surface mixing layer extends into 10–15 m depths during most of the growing season.

A one-pot enzymatic 13C-labeling method for the 3-position of sialic acid (NeuAc) analogues has been developed using NeuAc aldolase, lactate dehydrogenase (LDH), alcohol dehydrogenase (ADH), and nucleotide pyrophosphatase (NPP). This method consists of two steps, the first of which is degradation to 2-acetamido-2-deoxy-d-mannose (ManNAc) analogues. This degradation reaction was accelerated by a cofactor regeneration system which converts pyruvic acid into lactic acid using LDH, ADH, and β-nicotinamide adenine dinucleotide oxidized form (β-NAD+). The second step is condensation of the ManNAc analogue with [3-13C]-pyruvic acid newly added after decomposition of the cofactor by nucleotide pyrophosphatase which play a role like switch to stop conversion of pyruvic acid into lactic acid. Five different NeuAc analogues have been labeled in good yields using this newly developed one-pot enzymatic procedure. Following conversion of [3-13C]-NeuAc to CMP-[3-13C]-NeuAc, enzymatic synthesis of [3-13C]-NeuAc-α-(2→3)-[U-13C]-Gal-β-(1→4)-GlcNAc-β-x-ovalbumin (x: hybrid type oligosaccharide) 23 and [3-13C]-NeuAc-α-(2→3)-[U-13C]-Gal-β-(1→4)-GlcNAc-β-OMe 26 (sialyl LacNAc) was performed using bovine β-1,4-galactosyltransferase and rat recombinant α-2,3-sialyltransferase. The 1H chemical shifts of all protons in [3-13C]-NeuAc-α-(2→3)-[U-13C]-Gal-β- on a glycoprotein were assigned by 2D HMQC, 1D HSQC-TOCSY, and the herein described 1D and 2D HSQC-TOCSY-NOESY-TOCSY method. More specifically, the 7-, 8-, and 9-protons of NeuAc could be observed by this HSQC-TOCSY-NOESY-TOCSY method even with only a single 13C atom at the 3-position. In addition, 1D and 2D HMQC-NOESY spectra as well as carbon spin−lattice relaxation times (T 1) were measured to compare the conformational properties and dynamic behavior of the sialylgalactoside as part of the sialyl LacNAc 26 and when bound to a glycoprotein 23. These analyses suggested that the conformational properties of sialyl LacNAc are similar for both the conjugated and unconjugated forms, and that the torsional angle of the sialyl linkage, i.e., COOH−C2NeuAc−O−C3Gal, is biased toward the anti (−146.7°) conformation. In addition, the flexibility of galactosyl ring when bound to a glycoprotein appears to be significantly restricted by the attachment of NeuAc as compared with unconjugated sialyl LacNAc.

It is widely reported that derivatives of sugar moieties can be used to metabolically label cell surface carbohydrates or inhibit a particular glycosylation. However, few studies address the effect of substitution of the cytidylmonophosphate (CMP) portion on sialyltransferase activities. Here we first synthesized 2'-O-methyl CMP and 5-methyl CMP and then asked if these CMP derivatives are recognized by alpha2,3-sialyltransferases (ST3Gal-III and ST3Gal-IV), alpha2,6-sialyltransferase (ST6Gal-I), and alpha2,8-sialyltransferase (ST8Sia-II, ST8Sia-III, and ST8Sia-IV). We found that ST3Gal-III and ST3Gal-IV but not ST6Gal-I was inhibited by 2'-O-methyl CMP as potently as by CMP, while ST3Gal-III, ST3Gal-IV, and ST6Gal-I were moderately inhibited by 5-methyl CMP. Previously, it was reported that polysialyltransferase ST8Sia-II but not ST8Sia-IV was inhibited by CMP N-butylneuraminic acid. We found that ST8Sia-IV as well as ST8Sia-II and ST8Sia-III are inhibited by 2'-O-methyl CMP as robustly as by CMP and moderately by 5-methyl CMP. Moreover, the addition of CMP, 2'-O-methyl CMP, and 5-methyl CMP to the culture medium resulted in the decrease of polysialic acid expression on the cell surface and NCAM of Chinese hamster ovary cells. These results suggest that 2'-O-methyl CMP and 5-methyl CMP can be used to preferentially inhibit sialyltransferases, in particular, polysialyltransferases in vitro and in vivo. Such inhibition may be useful to determine the function of a carbohydrate synthesized by a specific sialyltransferase such as polysialyltransferase.

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