Page:Concepts for detection of extraterrestrial life.djvu/55

 CHAPTER XI

The multivator is a miniature laboratory for conducting a variety of biochemical or biological experiments on Mars. The nature of the experiments is limited only by those biological properties which can be measured by a photomultiplier as an output transducer. The device was conceived by Dr. Joshua Lederberg at Stanford University. The experiment which has received Dr. Lederberg’s particular attention is the detection of phosphatase activity. This is because:

1. phosphatase is widespread among terrestrial organisms;

2. it catalyzes the hydrolysis of phosphate esters with moderate specificity;

3. it is involved with the role of phosphorus in metabolism and energy transfer which may be a universal characteristic of carbon-based aqueous living systems; and

4. it is capable of being detected with relatively high sensitivity.

A functional test for the presence of hydrolytic enzymes, such as phosphatase, detects the catalysis of. The basis of the phosphatase test is the release of AH which differs from AB in being fluorescent. In this case, A is a fluorescent residue and B is a phosphate that permits the fluorometric assay of phosphatase. The multivator is designed to carry out such assays as well as many others. It does this by mimicking in miniature a great many of the kinds of instruments used in a typical biochemical laboratory. The basic elements of the instruments are a light source followed by a filter; the sample under investigation; another filter centered at either the same wavelength as the excitation filter for colorimetry or light scattering, or at a different wavelength if fluorometric observations are to be made; and finally, a light detector, usually a photomultiplier. Figure 16 shows several cut-away views of the multivator.

The most recent version of the multivator consists of 15 modules arranged in a circle around an impeller (figs. 17 and 18). Each of the modules basically 45