In this theory of kinetics, stationary state of intermediate complex, [ES] is
assumed. Therefore k +1 [ES] À (k À1 + k +2 )[ES] ¼ 0 and ES
½ ¼
E
½ 0
K m þ S
½ is obtained
by replaced by [E] ¼ [E] 0 -[ES]. Finally, v ¼ k þ2 ES
½ ¼
k þ2 E
½ 0 S
½
K m þ S
½ ¼
V max S
½
K m þ S
½ is obtained.
5.5 Regulation of Enzyme Activity
Cell, essential unit of life, provides regulation mechanism to maintain homeostasis.
And system of chemical reaction in cell is composed of enormous number of
enzymes. Therefore, maintaining homeostasis is mainly due to regulation of
enzymes.
5.5.1 Control of Enzyme Amount
Amount of enzyme is controlled to keep balance between synthesis and degradation,
and control of synthesis is due to operon mechanism. Parade et al. suggested
existence of repressor in 1959, and F. Jacob J. Monod proposed operon theory in
1961 [3]. Operon theory was proposed as lactose operon in prokaryote, E.Coli. And
study of operon is extended to study of promoter including regulation mechanism of
eukaryotes. Processing of mRNA is also studied in prokaryotes. On the other hand,
regulation by degradation of enzymes is studied for various proteases such as Ca
2+ -
dependent protease.
5.5.2 Control of Enzyme Activity
There is feedback inhibition that final product in metabolic pathway suppresses an
activity of enzyme locating on preceding pathway. There are two types of control
mechanism using nucleotide. Nucleotide-1-phosphate is bound on enzyme in bacteria or phosphate moiety is transferred from ATP to OH group of specific amino
acid such as serine, threonine and tyrosine in enzyme of eukaryote by protein kinase.
And these modifications of enzyme induce conformational change of enzyme and
results in regulation of enzyme activity. Regulation by protein kinase is also
important mechanism for regulation of functional protein. And the bound phosphate
is dissociated by phosphatase to recover the activity to original state. Protein kinase
was found by Burnett and Kennedy in 1954. They found protein kinase activity of
phosphorylation of casein in rat liver in 1954. There are other protein kinases such as
cyclic AMP dependent protein kinase, cyclic GMP dependent protein kinase, Ca
2+
dependent protein kinase and double strand RNA dependent protein kinase.
5.5 Regulation of Enzyme Activity
75
assumed. Therefore k +1 [ES] À (k À1 + k +2 )[ES] ¼ 0 and ES
½ ¼
E
½ 0
K m þ S
½ is obtained
by replaced by [E] ¼ [E] 0 -[ES]. Finally, v ¼ k þ2 ES
½ ¼
k þ2 E
½ 0 S
½
K m þ S
½ ¼
V max S
½
K m þ S
½ is obtained.
5.5 Regulation of Enzyme Activity
Cell, essential unit of life, provides regulation mechanism to maintain homeostasis.
And system of chemical reaction in cell is composed of enormous number of
enzymes. Therefore, maintaining homeostasis is mainly due to regulation of
enzymes.
5.5.1 Control of Enzyme Amount
Amount of enzyme is controlled to keep balance between synthesis and degradation,
and control of synthesis is due to operon mechanism. Parade et al. suggested
existence of repressor in 1959, and F. Jacob J. Monod proposed operon theory in
1961 [3]. Operon theory was proposed as lactose operon in prokaryote, E.Coli. And
study of operon is extended to study of promoter including regulation mechanism of
eukaryotes. Processing of mRNA is also studied in prokaryotes. On the other hand,
regulation by degradation of enzymes is studied for various proteases such as Ca
2+ -
dependent protease.
5.5.2 Control of Enzyme Activity
There is feedback inhibition that final product in metabolic pathway suppresses an
activity of enzyme locating on preceding pathway. There are two types of control
mechanism using nucleotide. Nucleotide-1-phosphate is bound on enzyme in bacteria or phosphate moiety is transferred from ATP to OH group of specific amino
acid such as serine, threonine and tyrosine in enzyme of eukaryote by protein kinase.
And these modifications of enzyme induce conformational change of enzyme and
results in regulation of enzyme activity. Regulation by protein kinase is also
important mechanism for regulation of functional protein. And the bound phosphate
is dissociated by phosphatase to recover the activity to original state. Protein kinase
was found by Burnett and Kennedy in 1954. They found protein kinase activity of
phosphorylation of casein in rat liver in 1954. There are other protein kinases such as
cyclic AMP dependent protein kinase, cyclic GMP dependent protein kinase, Ca
2+
dependent protein kinase and double strand RNA dependent protein kinase.
5.5 Regulation of Enzyme Activity
75