NDP‐sugars, floridoside and floridean starch levels in relation to activities of UDP‐glucose pyrophosphorylase and UDP‐glucose‐4‐epimerase in Solieria chorda l is (Rhodophyceae) under experimental conditions

Abstract

SUMMARY Under limited nutrient availability (i.e. unenriched sea‐water) and under 75 mol photons m–2 s–1 irradiance 12:12 LD, thalli of Solieria chordalis J. Agardh accumulated floridean starch and floridoside. When they were transferred into nutrient‐enriched seawater (150 umol L−1 NO31‐ and 7 umol L−1 P043i at 35 umol photons m−2 s−1 in irradiance 12:12 LD, starch and floridoside levels decreased. The main nucleotide diphosphate (NDP) sugars (i.e. UDP‐glucose, UDP‐galactose and ADP‐glucose) and the activities of UDP‐glucose pyrophosphorylase [Enzyme Code (EC) 2.7.7.9] and UDP‐glucose‐4‐epimerase (EC 5.1.3.2) were measured under these controlled culture conditions. Both UDP‐glucose and UDP‐galactose in the thal l i increased under conditions known to favor the accumulation of floridean starch and floridoside, whereas they decreased under conditions leading to floridean starch and floridoside breakdown. On the other hand, ADP‐glucose level only varied slightly. Although UDP‐glucose pyrophosphorylase activity rose under conditions of floridean starch synthesis, little variation was observed in UDP‐glucose‐4‐epimerase activity. These results suggest a possible enzymatic regulation of the NDP‐sugar and carbohydrate pool in which UDP‐glucose pyrophosphorylase would play a major role.

EFFECT OF NUTRIENT DEPRIVATION AND RESUPPLY ON METABOLITES AND ENZYMES RELATED TO CARBON ALLOCATION IN GRACILARIA TENUISTIPITATA (RHODOPHYTA)1

“…However, one possible mechanism for regulation of carbon allocation resides in the relative rates of UDPGlc/UDPGal synthesis/utilization. In a similar experiment conducted on the carrageenophyte Soleria chordalis, Goulard et al (2001) activity. These authors also observed an increase in both UDPGlc and UDPGal during nutrient limitation, similarly to what we observe during the first 6 days of nutrient limitation in our conditions.…”

Floridean Starch and Floridoside Metabolic Pathways of Neoporphyra haitanensis and Their Regulatory Mechanism under Continuous Darkness

“…Floridoside (α-d-galactopyranosyl-(1,2)-glycerol), a natural galactosyl glycerol, is the main common soluble photosynthetic molecule synthesized in red algae cytoplasm, and exhibits prebiotic characteristics in vitro [17,18]. Isofloridoside, an enantiomeric form of floridoside, has two isomeric forms: D-and L-isofloridoside [19].…”

Structural Diversity in Galactans From Red Seaweeds and Its Influence on Rheological Properties

“…An existing carbohydrate pool of floridean starch and floridoside. Floridean starch is the main reserve polysaccharide of red macroalgae, which is degraded during respiration to form UDP- d -glucose via UDP- d -glucose pyrophosphorylase ( Lluisma and Ragan, 1999 ; Goulard et al., 2001 ). The enzyme UDP-galactose 4-epimerase, subsequently interconverts UDP- d -glucose to UDP- d -galactose ( Frey, 1996 ).…”