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H M Kalckar

Publications and source records attributed to H M Kalckar.

At least 55 records · Page 3Linked to original sources
PubMed1971

The periplasmic galactose binding protein of Escherichia coli.

A specific high affinity galactose transport system called P(betag) can be induced by trace amounts of galactose in the medium by virtue of its own ability to capture and accumulate galactose. The transport system is coregulated with the production of a high affinity periplasmic galactose binding protein, which constitutes but one part of the transport system. Some transport negative mutants still remain producers of this binding protein. A close correlation exists between production of the active binding protein and the presence of galactose chemotaxis. The hypothesis, that this binding protein is a common element of the specific galactose transport system, P(betag), and of galactose chemotaxis is supported by observations on structural mutants, being defective in galactose binding protein as well as showing a lack of galactose chemotaxis. The binding protein is a monomer with two binding sites for galactose. Binding of one or two of the galactose molecules elicits specific conformational changes of the galactose binding protein (lowered affinity for galactose, increase of charges of the protein, increased fluorescence of tryptophan residues). The importance of these features for transport and for chemotaxis is discussed (70).

Bacterial Proteins↗
PubMed1970

The reductive inactivation of UDPgalactose-4-epimerase from yeast and E. coli.

The prosthetic groups of UDPgalactose-4-epimerase from yeast and E. coli can be reduced by incubation with D-galactose or L-arabinose provided that 5' uridylic acid (5'UMP) is also present. This type of concerted reduction can also be performed using sodium borohydride. The latter type of reduction also depends on the addition of 5'UMP. Enzymatic analysis of the released prosthetic group by means of lactic dehydrogenase and pyruvate revealed that the pyridine nucleotide of the reduced epimerase generated in the concerted reaction is dehydrogenated in the 4-position of the pyridine ring. The catalytic activity of the reduced epimerase is much lower than that of epimerase (10-15% of native epimerase). This reductive inactivation was also found in crude epimerase preparations from E. coli, again provided 5'UMP is present. Fractionated E. coli epimerase subjected to the concerted reduction show a striking fluorescent enhancement of the order of magnitude of that observed in the purified yeast epimerase. Unlike the latter, however, E. coli epimerase also becomes fluorescent upon addition of the specific substrate UDPgalactose. The physiological aspects of the phenomenon as related to induction of the galactose genes is discussed.

Arabinose↗