Synthases catalyze condensation
reactions in which no nucleoside triphosphate (ATP, GTP, and so forth) is
required as an energy source. e.g. Citrate synthase
Synthetases catalyze
condensations that do use
ATP or another nucleoside triphosphate as a source of energy for the synthetic
reaction. Succinyl-CoA synthetase is such an enzyme.
Ligases are enzymes that
catalyze condensation reactions in which two atoms are joined using ATP or
another energy source. (Thus synthetases are ligases.) DNA ligase, for example,
closes breaks in DNA molecules, using energy supplied by either ATP or NAD+; it is widely used
in joining DNA pieces for genetic engineering.
Ligases are not to be confused with lyases, enzymes that
catalyze cleavages (or, in the reverse direction, additions) in which
electronic rearrangements occur. The PDH complex, which oxidatively cleaves CO2
from pyruvate, is a member of the large class of lyases.
The name kinase is applied to enzymes that transfer a phosphoryl group from a
nucleoside triphosphate such as ATP to an acceptor molecule—a sugar (as in hexokinase
and glucokinase), a protein (as in glycogen phosphorylase kinase), another
nucleotide (as in nucleoside diphosphate kinase), or a metabolic intermediate
such as oxaloacetate (as in PEP carboxykinase). The reaction catalyzed by a
kinase is a phosphorylation.
On the other hand, phosphorolysis
is a displacement reaction in which
phosphate is the attacking species and becomes covalently attached at the point
of bond breakage. Such reactions are catalyzed by phosphorylases. Glycogen
phosphorylase, for example, catalyzes the phosphorolysis of glycogen, producing
glucose 1-phosphate.
Dephosphorylation, the
removal of a phosphoryl group from a phosphate ester, is catalyzed by phosphatases, with
water as the attacking species. Fructose bisphosphatase-1 converts fructose
1,6-bisphosphate to fructose 6-phosphate in gluconeogenesis, and phosphorylase a phosphatase removes
phosphoryl groups from phosphoserine in phosphorylated glycogen phosphorylase.
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ReplyDeleteNote that, originally, biochemical nomenclature distinguished synthetases and synthases. Under the original definition, synthases do not use energy from nucleoside triphosphates (such as ATP, GTP, CTP, TTP, and UTP), whereas synthetases do use nucleoside triphosphates. It is also said that a synthase is a lyase (a lyase is an enzyme that catalyzes the breaking of various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond or a new ring structure) and does not require any energy, whereas a synthetase is a ligase (a ligase is an enzyme that binds two chemicals or compounds) and thus requires energy.
Enzymatics' high-concentration T4 DNA ligase in combination with the 2X Rapid Ligation buffer greatly stimulates the rate and efficiency blunt-end ligation, therefore long incubations (>10 minutes) are NOT recommended and can greatly reduce the transformation efficiency of ligation products. In order to maximize transformation efficiency of the correct insert/vector combination, the following protocol is recommended.