Working with mouse cell lines you isolated a line that lacks the ribonuclease A (RNAse A) activity. After sequencing the mutant gene. you identified a single nucleotide change resulting in the substitution of a tyrosine instead of a cystine in the peptide sequence. The normal mouse RNAse A has 8 cysteines.
Using your knowledge of protein structure, explain why you think the cell line lacks RNAse A activity