Substrate Oxidation

Question 1

What is required in order to measure labelling of a 13C substrate?

Answer 1

• Compunds need to be volatile for gas chromatographic separation

Question 2

How does GC separate complex mixtures?

Answer 2

• By increasing the temperature of the oven so compound becomes volatile and flows through the column into the mass spec
• compound is fragmented which allows for compound identification and measurement of 13 C in the compound

Question 3

What is 13C?

Answer 3

• precursor for oxidation, either phenylalanine or glucose

Question 4

What is continous flow-isotope ratio mass spec (CF-IRMS)?

Answer 4

• allows us to measure 13C labelling of C02 in breath samples (directly)

Question 5

Why is the observation/application of indirect calorimetry important?

Answer 5

used to measure energy expenditure and fuel selection/utilisation

Question 6

Explain the steps for indirect calorimetry

Answer 6

• Willing volunteer set up for measurements of breath gas
• Baseline measures of RER over 20-30 mins are made prior to the ingestion of a liquid meal
• Weight, age ans sex is measured to allow the calculation of various parameters
• volunteer lies on a bed with a plastic canopy placed over the head whilst breath gases are analysed
• Volunteers asked to drink a liquid meal to demonstrate the effect of a meal on enerfy expenditure and substrate utilisation

Question 6

What is Weir formula?

Answer 6

Restinh metabolic rate (kcal/day) = 1.44 (3.94 VO2 + 1.11 VCO2)

Question 7

What is Respiratory Quotient?

Answer 7

RQ = VCO2/Vo2
RQ of 1 = Glucose metabolism
RQ of 0.7 = Fat metabolism

Question 8

What is F13CO2?

Answer 8

F13CO2 = VCO2 x CO2 enrichment
- the rate of appearance of 13CO2 in breath

Question 9

How do we use doubly labelled water (DLW) 2H218O to assess EE “Gold-standard approach”?

Answer 9

• Rate of CO2 production - differnece in rate of 2H and 18 O losses
• RQ- daily avg - o.85
• Determine rate of VO2
• Input to Weir formula