Substration Oxidation (PRACTICAL)

Question 1

what are 2 mass spectrometry methods and what are they used as a precursors for?

Answer 1

• Gas chromatography-mass spectrometry: used to measure precursor labelling
• stable-isotope mass spectrometry: used in analysis of breath samples

Question 2

to measure 13C substrate labelling, what do you need to do to the compounds for gas chromatographic separation

Answer 2

need to make them volatile for gas chromatographic separation

Question 3

as glucose and phenylalanine are solid powders at room temp, what do we need to do to them to make them more volatile and less polar?

Answer 3

we need to derivatize them (turn them into derivatives)

Question 4

outline in 3 steps how gas chromatography separates complex mixtures and allows you to identify the compound, and also state the precursor of oxidation

Answer 4

1. seperates complex mixtures by increasing the temperature of the oven
2. the compound becomes volatile and flows through the column into the mass spectrometer,
3. this fragments the compound, allowing you to identify the compound (from its mass spectrum) and also measure the amount of 13C in the compound

• 13C is the precursor for oxidation

Question 5

what does continuous-flow isotope ratio mass spectrometry (CF-IRMS) allow us to measure?

Answer 5

allows us to measure the 13C labelling of CO2 in breath samples

Question 6

how does isotope ratio mass spectrometry work?

Answer 6

• system that separates N2, O2 and CO2 gases by chromatography and then passes them into a mass spectrometer for isotope ratio analysis of CO2.

Question 7

how many detectors are there in continuous flow isotope ratio mass spectrometry and what mass are they looking for in the gas sample that denotes 13C?

Answer 7

• 3 detectors
• looking for mass 45

Question 8

outline the 4 steps is the gold-standard approach to assess energy expenditure?

Answer 8

1. calculate rate of CO2 production (VCO2), by looking at difference in rate of ^2H and ^18O losses from doubly labelled water
2. RQ daily average is 0.85
3. Do VCO2/RQ to determine VO2
4. input VCO2 and VO2 into the weir formula to determine energy expenditure

Question 9

what is the weir formula

Answer 9

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

Question 10

how do you calculate respiratory quotient?

Answer 10

RQ = VCO2/VO2

Question 11

what does a RQ of 1 mean?

Answer 11

that the body has selected glucose metabolism as the fuel source

Question 12

what does an RQ of 0.7 mean?

Answer 12

that the body has selected fat metabolism as the fuel source

Question 13

what is rate of CO2 production (VCO2) equal to?

Answer 13

equal to difference in rate ^2H and ^18O losses from doubly labelled water

Question 14

what is F13CO2 and what does it allow for?

Answer 14

the rate at which the 13C labelled substrate (glucose, fatty acids or amino acids) are being oxidised

Question 15

what is the equation linking F13CO2, VCO2 and CO2 enrichment

Answer 15

F13CO2 = VCO2 x CO2

Question 16

what are the 2 methods to calculate Energy expenditure

Answer 16

• using double labelled water
• 13C labelled substrate drink

Question 17

what is respiratory quotient

Answer 17

the ratio of volume of CO2 production vs volume of Oxygen consumption