Premium
Regulation of Carbohydrate Metabolism During Giardia Encystment 1
Author(s) -
JARROLL EDWARD L.,
MACECHKO P. TIMOTHY,
STEIMLE PAUL A.,
BULIK DOROTA,
KARR CRAIG D.,
KEULEN HARRY,
PAGET TIMOTHY A.,
GERWIG GERRIT,
KAMERLING JOHANNES,
VLIEGENTHART JOHANNES,
ERLANDSEN STANLEY
Publication year - 2001
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.2001.tb00412.x
Subject(s) - biology , glucosamine , enzyme , biochemistry , giardia , biosynthesis , galactosamine , polysaccharide , transferase , metabolism , microbiology and biotechnology
.Giardia intestinalis trophozoites encyst when they are exposed to bile. During encystment, events related to the inducible synthesis of a novel N‐acetyl‐ d ‐galactosamine (GalNAc) homopolymer, occur. Within the first 6 h of encystment, mRNA for glucosamine 6‐P isomerase (GPI), the first inducible enzyme unique to this pathway appears, oxygen uptake rates double from non‐encysting levels, and metronidazole (MTZ) inhibits oxygen uptake. Within 12 h, GPI and its activity are detectable and OU decreases 50% from non‐encysting levels; glucose's stimulation and MTZ's inhibition of oxygen uptake cease. In contrast, aspartate uptake remained constant throughout the 40 h monitored. Two genes, gpi 1 and 2 encode for GPI, but only gpi l is expressed during encystment. Glucosamine 6‐P (GlcN6P), the synthetic product of GPI, activates UDP‐N‐acetylglucosamine (UDP‐GlcNAc) pyrophosphorylase, a downstream enzyme, 3 to 5‐fold in the direction of UDP‐GlcNAc synthesis. UDP‐GlcNAc is epimerized to UDP‐GalNAc and UDP‐GalNAc is polymerized by “cyst wall synthase” (β 1 → 3 GalNAc transferase) into a highly insoluble β 1,3‐linked homopolymer. This GalNAc polysaccharide, the major component of cyst wall filaments, forms, in conjunction with polypeptides, the outer cyst wall of Giardia .