Purification and properties of guanosine 5', 3'-polyphosphate synthetase from Bacillus brevis.

A ribosome-independent guanosine 5',3'-polyphosphate synthetase has been highly purified from Bacillus brevis (ATCC 8185). The enzyme has a molecular weight of 55,000, as measured by sucrose density gradient centrifugation. Like the ribosome-connected stringent factor of Escherichia coli, it catalyzes the synthesis of the guanosine 5', 3'-polyphosphates by a pyrophosphoryl transfer mechanism from adenosine triphosphate (ATP) to guanosine di- or triphosphates (GDP, GTP). It has an apparent Km of 0.14 mM for GDP and 0.77 mM for GTP, and is specific for the guanosine ribonucleotides as pyrophosphoryl acceptors. Several ATP analogues were tested for their ability to donate the pyrophosphoryl group. Mg2+ was required as a counter ion for the nucleotide substrate; however, an excess of Mg2+ was inhibitory. The property of the B. brevis enzyme is compared with the ribosome-linked enzyme of E. coli and an extracellular enzyme excreted by several types of Streptomyces reported upon recently.     

Lactation physiology: A ruminant animal perspective

Summary Importance of peripubertal mammary development as a foundation for subsequent mammary growth and milk production was discussed. Morphological differences in peripubertal mammary growth in rodents and ruminants were described. The relevance of tissue interactions and association with hormones and growth factors in mammary development were delineated. Data from specific studies with ruminant mammary parenchyma were outlined for comparison with rodent studies. It is concluded that the wholesale extrapolation of data from rodent studies to explain udder development is inappropriate. Lastly, recent data from experiments with culture of mammary explants from bulls is described. Pragmatically, these data suggest that responses of mammary tissue from bulls might provide a means for early selection of superior sires or provide a unique model to study tissue interactions in udder development.It has been a pleasure for me to have the opportunity to prepare this paper in honor of Dr. Stuart Patton on his 70th birthday. Dr. Patton, one of the founders of the Gordon Conference on Mammary Gland Biology, had the vision to bring together the variety of workers interested in the mammary gland and drive to foster wide ranging collaborations.