Linked Life Data

9578601

Source:http://linkedlifedata.com/resource/pubmed/id/9578601

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
1
pubmed:dateCreated
1998-6-8
pubmed:databankReference
pubmed:abstractText
Comparison of the protein sequences deduced from the cDNAs of maize granule-bound starch synthase, Escherichia coli glycogen synthase, and maize starch synthase I (SSI) reveals that maize SSI contains an N-terminal extension of 93 amino acids. In order to study the properties of maize SSI and to understand the functions of the maize SSI N-terminal extension, the gene coding for full-length SSI (SSI-1) and genes coding for N-terminally truncated SSI (SSI-2 and SSI-3) were individually expressed in E. coli. Here we describe for the first time the purification of a higher plant starch synthase to apparent homogeneity. Its kinetic properties were therefore studied in the absence of interfering amylolytic enzymes. The specific activities of the purified SSI-1, SSI-2, and SSI-3 were 22.5, 33.4, and 26.3 micromol Glc/min/mg of protein, respectively, which are eight times higher than those of partially purified SSI from developing maize endosperm. The full-length recombinant enzyme SSI-1 exhibited properties similar to those of the enzyme from maize endosperm. As observed for native maize enzyme, recombinant SSI-1 exhibited "unprimed" activity without added primer in the presence of 0.5 M citrate. Our results have clearly indicated that the catalytic center of SSI is not located in its N-terminal extension. However, N-terminal truncation decreased the enzyme affinity for amylopectin, with the Km for amylopectin of the truncated SSI-3 being about 60-90% higher than that of the full-length SSI-1. These results suggest that the N-terminal extension in SSI may not be directly involved in enzyme catalysis, but may instead regulate the enzyme binding of alpha-glucans. Additionally, the N-terminal extension may play a role in determining the localization of SSI to specific portions of the starch granule or it may regulate its interactions with other enzymes involved in starch synthesis.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0003-9861
pubmed:author
pubmed:copyrightInfo
Copyright 1998 Academic Press.
pubmed:issnType
Print
pubmed:day
1
pubmed:volume
353
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
64-72
pubmed:dateRevised
2002-11-1
pubmed:meshHeading
pubmed:year
1998
pubmed:articleTitle
Purification and characterization of maize starch synthase I and its truncated forms.
pubmed:affiliation
ExSeed Genetics, L.L.C., Iowa State University, Food Science Building, Ames, Iowa 50011, USA.
pubmed:publicationType
Journal Article