**Question:** All enzyme activity is increased in fasting state Except

A. Peptidylglycine alpha-amidating monooxygenase (PAM)
B. Glucose-6-phosphatase
C. Alanine aminotransferase (ALT)
D. Alanine transaminase (ALT)

**Core Concept:** Enzymes are proteins that act as biological catalysts, speeding up chemical reactions within the body. Enzyme activity is influenced by various factors, including nutritional status (e.g., fasting). Generally, enzyme activity increases during fasting due to reduced competition from other substrates and cofactors.

**Why the Correct Answer is Right:** In this case, the correct answer, D. Alanine transaminase (ALT), is the only enzyme from the given options whose activity is decreased in the fasting state. ALT is an enzyme involved in the gluconeogenesis process, which occurs primarily in the liver and helps maintain glucose homeostasis during fasting. Since gluconeogenesis is suppressed during fasting, ALT activity decreases as well.

**Why Each Wrong Option is Incorrect:** Let's examine the other options:

A. PAM (Peptidylglycine alpha-amidating monooxygenase) is involved in the synthesis of biogenic amines, particularly in the adrenal cortex. Fasting does not significantly affect PAM activity, as this enzyme's function is unrelated to the primary hormonal changes occurring during fasting.

B. Glucose-6-phosphatase is an enzyme involved in the gluconeogenesis process, which is increased in the fasting state. Thus, its activity decreases in fasting.

C. ALT (Alanine aminotransferase) activity decreases during fasting due to its role in gluconeogenesis.

D. ALT (Alanine aminotransferase) activity decreases in fasting because of its involvement in gluconeogenesis, which is suppressed during fasting.

**Clinical Pearl:** Understanding the effects of fasting on enzyme activity is crucial in interpreting liver function tests, especially when assessing liver dysfunction. A decrease in ALT levels during fasting is a crucial clue to differentiate between fasting-induced ALT decrease and liver dysfunction. Elevated ALT levels in the fasting state can imply liver dysfunction, while normal or decreased ALT indicates normal liver function during fasting.