Estrogens are plasma protein bound to albumin and/or sex hormone-binding globulin in the circulation. Some examples are sex hormone-binding globulin (SHBG), corticosteroid-binding globulin, and albumin. It is exclusively bound to albumin, with no binding to SHBG or corticosteroid-binding globulin. It is bound 65% to sex hormone-binding globulin (SHBG) and 33% bound weakly to albumin. It is a barrier to blood proteins such as albumin and globulin. Most are bound to thyroxine-binding globulin (about 70%), transthyretin (10%), and albumin (15%). It is derived from the precursor molecule angiotensinogen, a serum globulin produced in the liver. Similarly, hepatitis B immune globulin (HBIG) effectively prevents hepatitis B infection. Krugman injected students with gamma globulin, a type of antibody. The protein is called the corticosteroid-binding globulin (CBG). The proteins account for 5% of the serum globulin fraction. Estrogens induce the production of sex hormone-binding globulin (SHBG) in the liver. They account for about 10% of the globulin fraction of blood serum. One medicinal option suppresses testosterone by increasing the sex hormone-binding globulin. They constitute most of the gamma globulin fraction of the blood proteins.