Abstract: A sample is treated with a phosphoglyceric acid mutase (PGAM) inhibitor (polythionic acid (salt) such as potassium tetrathionate) to inactivate the M-type isozyme activity and the B-type PGAM is quantified by determining PGAM isozymes by a rate assay. The B-type PGAM is a novel marker for cerebral apoplexy, and the diagnosis of cerebral apoplexy is enabled by assaying it.

Abstract: Colored proteins having a known molecular weight of 1800 to 321200 are prepared by coupling monomers of a colored protein having a known molecular weight or by coupling a colored protein having a known molecular weight with a colorless protein having a known molecular weight. At least two proteins are selected from the so prepared colored proteins and used as a colored molecular weight marker. This colored molecular weight marker is used for determination of the molecular weight of a protein having an unknown molecular weight, and can also be used as a reference protein for purification of a protein having a known molecular weight.

Abstract: A group of compounds having the following general formula can be obtained by reacting chromoprotein and organic acid: ##STR1## wherein X is a chromophore, P is a protein, NH.sub.2 is mainly .epsilon.-amino group of lysine, n is a positive integer of 1 to 18, and m is a positive integer in the relation of m.ltoreq.n. This compound group has one to eighteen organic acids bonded thereto, and shows various isoelectric points in accordance with the number of the organic acids, but the respective isoelectric points are maintained constant. If such compounds each having an individual isoelectric point, are used as isoelectric point markers, it is possible to recognize accurately the position of isoelectric point only by a visual operation.

Abstract: 1,6-Dihydro nicotinamide adenine dinucleotide inhibits both H-type lactic dehydrogenase and M-type lactic dehydrogenase which are isoenzymes of lactic dehydrogenase, but the degree of inhibition thereof against H-type considerably differs from that against M-type. A ratio of H-type lactic dehydrogenase to M-type lactic dehydrogenase in serum can be measured by utilizing the difference of inhibition degree. Therefore we can diagnose the organ with trouble.

Abstract: Isoelectric point markers for a gel isoelectric separation are prepared to comprise at least two colored proteins of which the isoelectric point pHs are known and wherein the difference between the highest value and the lowest value among the said pHs is not less than 0.5. The markers are applied to analyze proteins in a gel isoelectric separation method. The method employing the said markers makes it easy to analyze proteins and shows an excellent performance.