Amine-Reactive and Photoreactive Cross-linkers

An important class of heterobifunctional reagents is the photoreactive cross-linkers that have one end that can be photolyzed to initiate coupling. Photoreactive cross- 

Suitable light sources for photolyzing include sunlamps manufactured by a number of companies, such as Philips Ultrapnil MLU 300 W, General Electric Sunlamp RSM 275 W, or National Self-Ballasted BHRF 240-250 V 250 W-P lamp. Irradiation for 15 min with such lamps while the sample is cooled in an ice bath will result in good photolysis of photoreactive cross-linkers and modification reagents. 

Although photoreactive aryl azides are relatively inert to thermochemical reactions prior to photolysis, they are not stable in the presence of sulfhydryl compounds, which can reduce the azide functional group to an amine. Avoid, therefore, the use of reduc-tants such as DTT or 2-mercaptoethanol before the photolyzing step, as these can react with the aryl azide within minutes (Staros etal., 1978). Avoid also amine-containing 

Of the following amine-reactive and photoreactive cross-linkers, the overwhelming majority use an aryl azide group as the photosensitive function. Only a few use alternative photoreactive chemical reactions, particularly perfluorinated aryl azide, benzophenone, or diazo compounds. For general background information on photoreactive cross-linkers see Das and Fox (1979), Kiehm and Ji (1977), Vanin and Ji (1981), Meijer et ai, 1988), and Brunner (1993). 

N-Hydroxysuccinimidyl-4-azidosalicylic acid (NFIS-ASA) is a heterobifunctional reagent containing an NHS ester on one end and a photoreactive aryl azide group on the 

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Finally, the small amine-reactive and photoreactive cross-linker NHS-ASA (Chapter 5, Section 3.1) can be iodinated to provide a nondeavable radioactive conjugate. 

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