Comparative sensitivity of 125I-protein A and enzyme-conjugated antibodies for detection of immunoblotted proteins

Comparative quantification of rat brain and pituitary angiotensin-converting enzyme with autoradiographic and enzymatic methods

Angiotensin-converting enzyme (ACE, kininase II, EC 3.4.15.1) was quantified in selected areas of the rat brain by 3 different methods. The enzyme activity was quantified by an enzymatic assay in homogenates of discrete brain areas with the use of the artificial substrate hippuryl-His-Leu-[14C]glycine. Binding of the specific ACE inhibitor [125I]351A was quantified after incubation of thin brain sections followed by quantitative autoradiography with comparison to [125I]standards. The antigenic sites of the enzyme were quantified by immunoautoradiography, using a polyclonal antibody to ACE in combination with [125I]protein A followed by quantitative autoradiography. There was a good correlation between the ACE activity, as determined by the quantitative enzymatic method, and both the enzyme inhibitor binding and the [125I]protein A binding, as determined by quantitative autoradiography, in brain areas and in anterior and posterior lobes of the pituitary gland. The present data demonstrate that ACE activity and ACE binding can be quantified in discrete tissue areas with different methods in a variety of conditions and with a high degree of accuracy.

Protein blotting: ten years on

Protein blotting was originally described in 1979 as an outgrowth of nucleic acid techniques, and received its commonly used designation of 'Western' blotting in 1981. The use of the technique to render electrophoresed proteins accessible for further analysis has found many roles, the most prominent being subsequent reaction with antibodies or antisera, which has many clinical and research applications. Since the initial development of the system there have been many changes to the techniques involved, but the basic principles remain unaltered. This review discusses these changes, and also provides a summary of current techniques.

A radioimmunohistochemical method for autoradiographic visualization of cell antigens using 125I-staphylococcal protein A

125I-Staphylococcal protein A was used to visualize immunoreactive cell antigen in rat brain and pituitary by autoradiography. Autoradiograms of rat brain sections generated with 125I-protein A were clear and showed low background signals. We were able to visualize neural structures containing tyrosine hydroxylase or methionine-enkephalin-like immunoreactivities in the brain, and vasopressin-like immunoreactivity in the pituitary gland. Our results suggest that 125I-protein A can be used for the radioimmunohistochemical visualization of cell antigens in tissue sections.

Radioimmunochemical methods for the quantitative autoradiographic determination of antigens in brain and other tissues

1. We have used horseradish peroxidase-conjugated protein A- and 125I-protein A to develop immunohistochemical and radioimmunohistochemical methods for the localization of antigens in brain and other tissues of the rat. 2. We visualized methionine-enkephalin fibers in the rat brain by incubating tissue sections with a specific polyclonal antibody and peroxidase-conjugated protein A. The method is simple, fast, and less expensive and more sensitive than classical immunohistochemical techniques and the principle could be used to visualize many other tissue antigens. 3. Incubation of tissue samples with specific polyclonal antibodies and 125I-protein A, followed by autoradiography, allows the permanent recording of the radioimmunohistochemical localization of brain methionine-enkephalin, tyrosine hydroxylase, and angiotensin-converting enzyme and of pituitary vasopressin and could be applied to the localization of many other tissue antigens. 4. A new quantitative radioimmunohistochemical technique for methionine-enkephalin allows the determination of the endogenous peptide content in discrete brain nuclei from 16-microns-thick sections. The method is based on the quantitative determination of the amount of 125I-protein A bound to specific tissue areas after incubation with a specific polyclonal antibody, followed by autoradiography and computerized microdensitometry. To quantify the endogenous peptide content, the values obtained are interpolated into a methionine-enkephalin internal standard curve. This standard curve was constructed by measuring endogenous concentrations of methionine-enkephalin by radioimmunoassay in specific brain regions and correlating these values with quantitative autoradiographic determinations in homologous areas of adjacent sections. Similar methods can be developed for other tissue antigens. 5. These new methods allow for the localization and quantification of tissue antigens in very discrete areas of the brain and other tissues and have a wide application in neurobiology and pathology.