By Billy Hammond (Copyright AELS)

July 3, 2021

Urea Cycle

I sometimes use urea as a nitrogen fertilizer for my plants. Every time I sprinkle it around my plants, being careful not to have it come into contact with them because of its caustic direct effect, I think back to the Urea Cycle I learned about decades ago in my college chemistry class.

The amino acids traveling around in the blood eventually make their way to the liver. Their nitrogen gets converted to urea there while the carbon atoms are oxidized to CO2 and H2O by various tissues.

In the Urea Cycle, NH4+, bicarbonate and ATP react together to form carbamoyl phosphate. This reacts with ornithine to form citrulline. Aspartate reacts with citrulline to form arginosuccinate, which releases fumarate thereby forming arginine. Arginase cleaves the arginine to release urea and regenerate ornithine.

尿素サイクル

野菜の窒素追加肥料として尿素を使うことがある。肥料をやりながら時々数十年前の大学の化学クラスを思い出す。その中で『尿素サイクル』を暗記した。血中のアミノ酸はいずれに肝臓にたどり着く。そこでアミノ酸の窒素が尿素に変換される。アミノ酸の炭素は組織内にCO2H2Oに酸化される。

尿素サイクルではNH4+、重炭酸塩 とATPが反応し、カルバモイルリン酸を形成する。カルバモイルリン酸はオルニチンと反応し、シトルリンが出来る。アスパラギン酸塩がシトルリンと反応、アルギニノコハク酸を形成し、フマル酸が放出し、アルギニンができる。アルギナーゼ はアルギニンを開裂し、尿素が放出と同時にオルニチンが再生される。

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English novels by Billy Hammond published by AELS

(AELS出版英語書籍リスト)

 

I. Majoh Gakuin and Hikari Juku – Japanese Witch Schools Trilogy

1. Majoh Gakuin & Hikari Juku – Japanese Witch Schools

2. Lost Witch (The second book)

3. Fate & Magic (The final book in the trilogy)

II. Brindle – Scryer Extraordinaire Trilogy

1. Brindle – Scryer Extraordinaire

2. Brindle – Scryer Extraordinaire – Returns

3. Brindle – Scryer Extraordinaire – Challenges (The final book in the trilogy)

III. Fantasy fiction set in Japan

1. 21st Century Ninja

2. Regressed

3. Japanese Woman

IV. Fantasy fiction set outside of Japan

1. Dimension Jumpers

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