Control of histidase formation and improvement of urocanic acid production inSerratia marcescens

Summary In the wild-type strain ofSerratia mar-cescens Sr41, histidase was subjected to both cata-bolite repression (CR) by glucose and nitrogen re-pression (NtR) by excess NH⁺ ₄. CR-or NtR-re-sistant mutants for histidase were isolated from urocanase-deficient strain Ud-8, which was more sensitive to CR and NtR than wild-type strain. CR-resistant strain Uc1016 showed a high forma-tion of histidase as well as of D-serine deaminase in the presence of glucose. However, the addition of 2% (NH₄)₂SO₄ to the minimal medium de-creased the histidase formation to a large extent. NtR-resistant strain Gcl98 showed a high forma-tion of histidase as well as of adenylylated glu-tamine synthetase even in the presence of glucose and excess NH⁺ ₄. NtR-resistant strain Gc2031, isolated from urocanic acid-producing strain UdT122, produced urocanic acid more rapidly than strain UdT122 and in proportion to the rate of growth, although the maximum amounts of urocanic acid produced were the same. During cultivation, histidine accumulation was less and histidase activity was four times higher in strain Gc2031 than in the strain UdT122.     

Recent advances in urocanic acid photochemistry, photobiology and photoimmunology.

Urocanic acid (UCA), produced in the upper layers of mammalian skin, is a major absorber of ultraviolet radiation (UVR). Originally thought to be a 'natural sunscreen', studies conducted a quarter of a century ago proposed that UCA may be a chromophore for the immunosuppression that follows exposure to UVR. With its intriguing photochemistry, its role in immunosuppression and skin cancer development, and skin barrier function, UCA continues to be the subject of intense research effort. This review summarises the photochemical, photobiological and photoimmunological findings regarding UCA, published since 1998.