A colorimetric method for determining low concentrations of mercaptans.

Ureases (urea amidohydrolases, EC 3.5.1.5) are a group of highly proficient enzymes, widely distributed in nature, whose catalytic function is to catalyze the hydrolysis of urea, its final products being carbonic acid and ammonia. The products and the resulting increase in pH of the reaction environment are consequential characteristics of the action of ureases. Apart from its natural significance, ureases-catalyzed hydrolysis of urea is important in that it has great potential for practical applications. In view of this importance, this article offers a review of the properties of the enzymes, where in addition to the established knowledge, the recent findings are presented. Special emphasis is put on the functional and practical properties of ureases that can be customized and exploited in a diversity of important applications, notably medical, analytical, environmental and engineering.

Ureases I. Functional, catalytic and kinetic properties: A review

The sulfhydryl groups of crystalline proteins. I. Some albumins, enzymes, and hemoglobins.

This article describes the identification of the enzyme nitrate reductase (NR) in the leaves of vascular plants. Although NR had previously been described in Neurospora, this is the first report of NR in plants. The discovery of NR opened up the field of study of plant nitrogen assimilation and led to the publication of hundreds of articles. NR requires reducing power from NADH, NADPH, or both depending on its location within the plant body and the species. This very complicated enzyme took many years to actually purify. After purification, we learned that it is controlled by phosphorylation/ dephosphorylation. Harold Evans and others later showed NR to be one of the few molybdenumcontaining enzymes in vascular plants. After working on NR, Evans turned his attention to another molybdenum-containing enzyme, dinitrogenase, in soybean (Glycine max) root nodule bacteroids. Harold Evans became President of the American Society of Plant Physiologists and a member of the National Academy of Science based on this discovery and many other contributions.

Francis P. Chinard

Papers

Protein sulfhydryl groups and the reversible inactivation of the enzyme urease the reducing groups of egg albumin and of urease

o-Iodosobenzoic Acid, a Reagent for the Estimation of Cysteine, Glutathione, and the Substituent Sulfhydryl Groups of Certain Proteins1

Determination of sulfhydryl groups in certain biological substances.