2. Calculate the protein molecular weight from the spectrum below, and identify all charge state for the below ESI spectrum (5)

Question

M/z
893.17
942.71
1060.44
848.54
1131.05
998.13
1211.77
808.17
1304.89
771.50
1413.58
737.99
1542.02

Answer 1

To calculate the molecular weight of the protein from the given ESI (Electrospray Ionization) spectrum data and identify its charge states, follow these steps:

1. Understanding the m/z values: The provided m/z values indicate the mass-to-charge ratios of ionized species of the protein. The charge state \( z \) can be determined based on the relative spacing of the m/z values.

2. Identifying charge states: For each m/z value:

   • The charge state \( z \) can be calculated as \( z = m/z \), where \( m \) is the molecular weight of the protein.
   • Using adjacent peaks to identify the charge states, we can recognize that the difference between m/z values should provide insight into the charge states.

3. Assuming different charge states for calculation:

   • If we assume the most common charge states to be 1, 2, or 3 (though higher charge states are possible), we can estimate the molecular weight accordingly.

4. Calculating the molecular weight using the highest m/z values:

   • For instance, using m/z 1542.02:
     • If \( z = 2 \) (common for larger proteins), then the molecular weight \( m \) can be estimated as: \[ m = z \times m/z = 2 \times 1542.02 = 3084.04 , \text{Da} \]
     • If \( z = 3 \), then: \[ m = 3 \times 1542.02 = 4626.06 , \text{Da} \]
     • If \( z = 1 \): \[ m = 1 \times 1542.02 = 1542.02 , \text{Da} \]

5. Identifying charge states for other m/z values:

   • We see the approximated differences between peaks; for example:
     • The difference between 893.17 and 848.54 is about 44.63, which suggests that they can be different charge states of the same protein.
   • By calculating \( (m/z_{next} - m/z_{current}) \):
     • For example, 942.71 and 899.17 difference is the same as 848.54 and 893.17.
   • Analyzing differences will help identify that the adjacent peaks are often spaced by roughly the same amount.

6. List of potential protein molecular weights and charge states:

   • Molecular weights from various charge states of the highest m/z (1542.02):
     • \( z = 1 \): 1542.02 Da
     • \( z = 2 \): 3084.04 Da
     • \( z = 3 \): 4626.06 Da

Using this analysis, assuming the highest m/z value provides the molecular weight, potential molecular weights of the protein from charge states of 1, 2, and 3 can be inferred based on the provided m/z spectrum data. The most likely charge state is often between 2 and 3, making the apparent mass around 3084 Da to 4626 Da based on presumption.

Conclusion:

• The estimated molecular weight of the protein is potentially between:
  • 1542.02 Da (z=1)
  • 3084.04 Da (z=2)
  • 4626.06 Da (z=3)
• Charge states can be identified where several peaks likely represent ionization states of the same molecule across the spectrum. Further analysis and evaluation of consistent patterns will enhance the accuracy of charge state determination.