---
title: "DU spectrophotometer"
chunk: 5/5
source: "https://en.wikipedia.org/wiki/DU_spectrophotometer"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:41:22.285535+00:00"
instance: "kb-cron"
---

=== Enzyme assays and DNA research ===
Gerty Cori and her husband Carl Ferdinand Cori won the Nobel Prize in Physiology or Medicine in 1947 in recognition of their work on enzymes. They made several discoveries critical to understanding carbohydrate metabolism, including the isolation and discovery of the Cori ester, glucose 1-phosphate, and the understanding of the Cori cycle. They determined that the enzyme phosphorylase catalyzes formation of glucose 1-phosphate, which is the beginning and ending step in the conversions of glycogen into glucose and blood glucose to glycogen. Gerty Cori was also the first to show that a defect in an enzyme can be the cause of a human genetic disease. The Beckman DU spectrophotometer was used in the Cori laboratory to calculate enzyme concentrations, including phosphorylase.
Another researcher who spent six months in 1947 at the Cori laboratory, "the most vibrant place in biochemistry" at that time, was Arthur Kornberg. Kornberg was already familiar with the DU spectrophotometer, which he had used at Severo Ochoa's laboratory at New York University. The "new and scarce" Beckman DU, loaned to Ochoa by the American Philosophical Society, was highly prized and in constant use. Kornberg used it to purify aconitase, an enzyme in the citric acid cycle.

"The enzyme could be assayed in a few minutes by coupling it to isocitrate dehydrogenase and in measuring the NADH formed using the Beckman DU spectrophotometer, an instrument that transformed biochemistry." 
Kornberg and Bernard L. Horecker used the Beckman DU spectrophotometer for enzyme assays measuring NADH and NADPH. They determined their extinction coefficients, establishing a basis for quantitative measurements in reactions involving nucleotides. This work became one of the most cited papers in biochemistry. Kornberg went on to study nucleotides in DNA synthesis, isolating the first DNA polymerizing enzyme (DNA polymerase I) in 1956 and receiving the Nobel Prize in Physiology or Medicine with Severo Ochoa in 1959.
The bases of DNA absorbed ultraviolet light near 260 nm. Inspired by the work of Oswald Avery on DNA, Erwin Chargaff used a DU spectrophotometer in the 1940s in measuring the relative concentrations of bases in DNA. Based on this research, he formulated Chargaff's rules. In the first complete quantitative analysis of DNA, he reported the near-equal correspondence of pairs of bases in DNA, with the number of guanine units equaling the number of cytosine units, and the number of adenine units equaling the number of thymine units. He further demonstrated that the relative amounts of guanine, cytosine, adenine and thymine varied between species. In 1952, Chargaff met Francis Crick and James D. Watson, discussing his findings with them. Watson and Crick built upon his ideas in their determination of the structure of DNA.

=== Biotechnology ===
Ultraviolet spectroscopy has wide applicability in molecular biology, particularly the study of photosynthesis. It has been used to study a wide variety of flowering plants and ferns by researchers in departments of biology, plant physiology and agriculture science as well as molecular genetics.
Particularly useful in detecting conjugated double bonds, the new technology made it possible for researchers like Ralph Holman and George O. Burr to study dietary fats, work that had significant implications for human diet. The DU spectrophotometer was also used in the study of steroids by researchers like Alejandro Zaffaroni, who helped to develop the birth control pill, the nicotine patch, and corticosteroids.

== Later models ==

The Beckman team eventually developed additional models, as well as a number of accessories or attachments which could be used to modify the DU for different types of work. One of the first accessories was a flame attachment with a more powerful photo multiplier to enable the user to examine flames such as potassium, sodium and cesium (1947).
In the 1950s, Beckman Instruments developed the DR and the DK, both of which were double-beam ultraviolet spectrophotometers. The DK was named for Wilbur I. Kaye, who developed it by modifying the DU to expand its range into the near-infrared. He did the initial work while at Tennessee Eastman Kodak, and later was hired by Beckman Instruments. The DKs introduced an automatic recording feature. The DK-1 used a non-linear scroll, and the DK-2 used a linear scroll to automatically record the spectra.
The DR incorporated a "robot operator" which would reset the knobs on the DU to complete a sequence of measurements at different wavelengths, just like a human operator would to generate results for a full spectrum. It used a linear shuttle with four positions, and a superstructure to change the knobs. It had a moving chart recorder to plot results, with red, green and black dots. The price of recording spectrophotometers was substantially higher than non-recording machines.
The DK was ten times faster than the DR, but not quite as accurate. It used a photomultiplier, which had introduced a source of error. The DK's speed made it preferred to the DR. Kaye eventually developed the DKU, combining infrared and ultraviolet features in one instrument, but it was more expensive than other models.
The last DU spectrophotometer was produced on July 6, 1976. By the 1980s, computers were being incorporated into scientific instruments such as Bausch & Lomb's Spectronic 2000 UV–Vis spectrophotometer, to improve data acquisition and provide instrument control. Specialized spectrophotometers designed for specific tasks now tend to be used rather than general "all-purpose machines" like the DU.

== References ==

== External links ==
Jaehnig, Kenton G. Finding Aid to the Beckman historical collection, 1911–2011 (bulk 1934–2004). Science History Institute. OCLC 899243886. Retrieved 6 February 2018. Links on landing page go to full documents.