Who identified the biochemical nature of transforming substance?

Options

A. Oswald Avery and Colin Macleod
B. Maclyn McCarty
C. F. Griffith
D. Both (1) and (2)

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the identification of the biochemical nature of the transforming substance, which refers to the genetic material responsible for transformation in bacteria.

2. **Historical Context**: The concept of the transforming principle was first introduced through experiments conducted by Frederick Griffith in 1928. He discovered that non-virulent bacteria could become virulent when exposed to heat-killed virulent bacteria.

3. **Key Experiments**:
- Griffith's experiment involved two strains of *Streptococcus pneumoniae*: the S-strain (virulent) and the R-strain (non-virulent).
- He found that when the R-strain was mixed with heat-killed S-strain bacteria, the R-strain transformed into virulent bacteria, indicating that some "transforming principle" was passed from the dead S-strain to the live R-strain.

4. **Further Identification**: Although Griffith identified the transformation phenomenon, he did not determine the biochemical nature of the transforming substance. This was later clarified by the work of Oswald Avery, Colin MacLeod, and Maclyn McCarty between 1933 and 1944.

5. **Avery, MacLeod, and McCarty's Contribution**: These scientists conducted experiments that demonstrated that DNA was the transforming substance. They showed that the transformation could be inhibited by enzymes that degrade DNA, confirming that DNA was responsible for carrying genetic information.

6. **Conclusion**: Therefore, while Griffith first observed the transformation, it was Avery, MacLeod, and McCarty who identified the biochemical nature of the transforming substance as DNA.

### Final Answer:
The biochemical nature of the transforming substance was identified by Oswald Avery, Colin MacLeod, and Maclyn McCarty.

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