15 内切酶及外切酶 $ 内切酶 A 3 4 5 # A 6 K 7 2 8 Q 9 10 J $ # 2 3 5 4 6 A A 7 8 K 9 ⌘ 内切酶：水解蛋白质肽链内部的一些肽键⌘ 外切酶：自肽链的末段开始每次水解一个氨基酸残基扩展：实验中常用的内切酶（蛋白，核酸）
16 酶原 6 A K 7 7 K A A A 7 6 A A 10 K K 10 10 Q 10 Q 10 Q 10 Q J J J J 酶原，无活性酶，有活性胃酸，胃蛋白酶胃蛋白酶胃蛋白酶原胰蛋白酶原糜蛋白酶原羧基肽酶原弹性蛋白酶原胰蛋白酶糜蛋白酶羧基肽酶弹性蛋白酶肠激酶酶原：酶的前体⌘ 可保护组织免受蛋白酶的自身消化作用。⌘ 保证酶在其特定的部位和环境发挥催化作用。⌘ 酶原还可视为酶的贮存形式。
36 Procaryotic vs Eucaryotic Procaryotes have a proteasome analog of that in eucaryotes but the function is unclear since ubiquitin has not been found. In procaryotes, all α subunits are identical and all β subunits identical whereas in eucaryotes these subunits exhibit a number of isoforms.Procaryotes do have a ubiquitin-like protein but it is is used in the synthesis of thiamine and not protein degradation.
59 Urea Cycle, Reaction 1Transfer of the carbamoyl group in the mitochondria.
60 Urea Cycle, Reaction 2A citrulline:ornithine antiport moves citrulline to the cytosol. The second NH2 for urea comes from Asp. An adenylated citrulline intermediate gives PPi.
61 Urea Cycle, Reaction 3Cleavage of fumarate, production of arginine
62 Urea Cycle, Reaction 4Cleavage of urea from arginine gives urea. The ornithine is ready to begin a new cycle.
63 Recycling to Aspartate Malate dehydrogenase occurs in mitochondria and in the cytosol.
64 N-AcetylglutamateN-AcGlu is synthesized when NH4+ levels increase during amino acid catabolism.An activator of CPS I which provides substrate for the urea cycle.Glu is a product of Gln hydrolysis by CPS II in pyrimidine synth.An intermediate in ornithine synthesis.
65 Structural similarity Blue - Ornithine transcarbamoylase from the urea cycleRed - Aspartate transcarbamoylase from pyrimidine synthesis
66 Functional similarity Transfer of an amino group by incorporation of aspartate and elimination of fumarate occurs in both the urea cycle and pyrimidine synthesis.