This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Medicine
Which of the following is the most likely effect of insulin at the cellular receptor level? 
Select and explain. 
A. stimulating tyrosine kinase, B. binding to ion channels, C. binding to intracellular erb A receptors, D. stimulating guanylate cyclase
A: stimulating tyrosine kinase
Answer: A: stimulating tyrosine kinase 
Explanation: Insulin binding to its receptor stimulates tyrosine kinase activity. Other stimulators of protein kinases include platelet-derived growth factor and epidermal growth factor. Tyrosine phosphorylation results from this interaction. Insulin-resistant states can be caused by pre-receptor resistance (mutated insulin, anti-insulin antibodies) or receptor and post receptor resistance.