Radioactive fermentation labeling of complex drugs, ligands, and recombinant proteins is a vital part of medical, agricultural, and molecular biology research. Custom fermentation with ¹⁴C, ³H, and ³⁵S isotopes, for example, provides cost-effective radiolabeling of many biologically active, complex molecules that are difficult to label using traditional organic synthesis. As a result, radioactive fermentation is becoming the method of choice for metabolism, toxicology and biodistribution applications. Each PerkinElmer custom fermentation is designed to enhance the specific activity of the final product and provide label in each region of the molecule. Our experts will help you select the most effective combination of microbial strain, radioactive substrate, and fermentation method needed to get the results you want. Plus, we can accurately monitor growth using proven analytical techniques.

Precursors for fermentation
PerkinElmer offers you a wide range of ¹⁴C, ³H, and ³⁵S precursors for use in custom fermentations. Buying the precursor and fermentation service together can significantly reduce your costs.

Submission of samples and confidentiality
With PerkinElmer's custom radioactive fermentation labeling, you supply the microbial strain and any information on optimal growth conditions and biohazards associated with the specific strain. We adhere to a policy of strict confidentiality, which covers the process, the microbial strain, and the final product. These, of course, remain proprietary to your organization. For added confidentiality, PerkinElmer may receive non-toxic media components as blind reagents.

Choice of radioactive substrate
The chemistry of the product and label position determines which radioactive substrate you choose. Because fermentation generally results in relatively low overall yields, on the order of 1% to 10%, there is a substantial amount of radioactive waste. So the best substrate is one that minimizes costs while maximizing yield. Also, substrate selection must take into account ¹⁴C oxidation to ¹⁴CO₂, ³H exchange with H₂O, and ³⁵S volatile generation, all of which present potential hazards if not adequately trapped. The procedure is designed to ensure safe handling from initial growth through radioactive labeling and downstream processing.

Generally, simple molecules such as [¹⁴C] acetate, propionate, and butyrate are preferred over complex molecules such as [¹⁴C(U)] glucose. In many Actinomycete macrolide antibiotic fermentations, [1-14C] acetate and [1-14C] propionate are particularly attractive substrates because they cost less and are readily available. For preparation of high specific activity radioactive proteins, the substrates - radioactive glucose and amino - acids are themselves fermentation products, and therefore more costly. Nucleic acid substrates such as [¹⁴C] thymine and [³H] thymine are successfully used in fermentation radiolabeling of plasmids, phage, and bacterial chromosomal DNA.

Fermentation quotations and project scheduling
All quotes are first subject to an assessment of Biological Hazards associated with the bacteria. Generally, we perform "test growths" first to validate assumptions used in preparing the quotation. Keep in mind that custom fermentation projects are done on a "first come-first served" basis, so you should place your orders well in advance.

Your input and on-site observation are welcomed at PerkinElmer
Chances are someone at your facility is knowledgeable about your products' chemistry and the unique characteristics of the strain of microorganism to be used in fermentation. If so, we suggest you assign an individual to interact directly with our scientists. This will eliminate the knowledge gaps that can interfere with the swift, cost-efficient execution of your custom fermentation. Ideally, this person should have some decision-making authority. You can also send a representative to PerkinElmer to observe your project in process. Just let us know in advance, for the sake of security and confidentiality.

Proper microorganism selection and metabolism
Choice of the most appropriate microbial strain is the key to ensuring maximal yield. Mutant strains or recombinant organisms may increase the level of expression. Using recombinant strains in fermentation ensures a higher level of expression. To properly assess the cost and safety of the fermentation, microbial metabolism must be given careful consideration.

Range of Substrate Choices
14C	Large number of available choices, including amino acids, sugars, nucleotides, and hydrocarbons.
3H	Large number of available choices, including amino acids, sugars, nucleotides, and hydrocarbons.
35S	Limited number of available choices: Z35S\ H2SO4: low cost, requires large amounts, not itself volatile. Z35S\ methionine or cysteine: easily incorporated into cells, but directly yields volatiles which require extensive trapping systems.
Specific Activity
14C	Relatively Low: 0.5 to 1.0 mCi/mg for proteins.
3H	High: 1 to 10 mCi/mg for proteins.
35S	Very High: 5 to 30 mCi/mg for proteins (depending on sulfur-containing amino acid content).
Relative Stability of Final Product
14C	Excellent stability.
3H	Moderate stability, decreasing with higher specific activity.
35S	Limited stability, must be used in 1-2 months.

Radiological safety considerations for custom fermentation
The ideal substrate for a custom fermentation generates the lowest level of radioactive volatiles, while providing the highest incorporation into the product. [1-14C] propionate is selected as the substrate when the biosynthesis involves polymerization of methylmalonate moieties. In protein labeling, [³⁵S] amino acids generate volatiles, which are trapped by proprietary methods. [¹⁴C(U)] D-Glucose generates volatiles with the resulting [¹⁴C]CO₂ trapped in sodium hydroxide. Our processes include containment redundancy to prevent environmental releases and protect the chemist.

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