A growth factor for cells was identified from extracts of rat brain. Preliminary characterization was done on this activity using several methods. Less than 5% of the activity could be precipitated by 80 % ammonium sulfate @ pH 7.5. Heat treatment ( 100 C for 10 minutes) had no effect on biological activity. On isoelectric focusing, the apparent isoelectric point of the active material was 4.8. By electrophoresis the growth factor was found to have a MW= 21,000. A. Based on the information given above, is this growth factor a protein? Explain. B. What other test could you do to confirm your answer in part a?